Interesting thread... there's a few ways I can go at this. I think I'll go straight into, being dropped into Yamaku into Mutou's class, and then it's me, not Hisao, rather than what would happen in each of the routes. There'll be some parallels to each end, though. And, I'll follow the general structure of befriending a girl and getting on her route, but the route would be VERY different in most cases.
Because there's no choice points any more, several of the existing choice points only acted to set Hisao's mindset up for an outcome, and had nothing to do with the actual outcome, meaning I can go completely against them.
One note is that I wouldn't hide my arrhythmia. That changes a few points.
Not sure if I'd introduce myself.
Shizune and Misha would annoy the crap out of me right off the bat. I'd keep them at arm's distance at least.
Rin would confuse the crap out of me. Just like she does in the VN. Arm's distance there, too. Basically, I'd treat her like Hisao does in Emi's route.
Lilly... now that gets interesting. The trick is that I would be put off by Lilly's excessive formality, and even less sure about how to conduct myself around her than Hisao was. And, back in high school, I would've convinced myself that she was way out of my league, and prevented myself from having (much) attraction to her, so that would close that route off. But, that doesn't necessarily close Hanako's route off, and I wouldn't be a dick to Lilly or avoid her, I'd just be put off a bit by her. I'm sure after a while of getting to know her, I could become friends with her, but certainly not in the first week.
Speaking of which, I'll get back to Hanako.
The Kenji route wouldn't happen. That asshole would get the door slammed in his face. My equivalent to the Kenji route would be sitting in my dorm room trolling IRC on my laptop.
As far as Hanako goes, it depends on a lot of variables. The trick would be if I felt attracted to her initially, nothing would happen - her social anxiety would likely keep her from approaching me, my anxiety around women that I'm attracted to would likely keep me from approaching her (especially given her tendency to bolt when stressed), and my distance from Lilly would keep her from pushing us together. If I didn't, however, things could get interesting, given the shared interests. What could happen is a few things like the library scene in the VN, as coincidental meetings. We'd find out about each other's interests, become friends, and I'd become attracted to her. And then I'd become worse than Hanako with my fear of rejection. Being her friend wouldn't be a problem, but I'd be tearing myself up over asking her out, to the point that I probably wouldn't friend-zone her the way Hisao did because I'd be too busy focusing on my own anxieties.
Speaking of which, her panic attack would probably send me into a panic attack. We'd feed off of each other's anxieties. If we could get past that, though...
Now that actually gets me close to the critical choice point for Hanako in the VN, and I could see that scene playing out like that. I'd want to spend time with Hanako, and I wouldn't be a dick and offer to and then pull it back... but not sure I'd go to the city. A bit of white knighting might slip in, but I'd do something with Hanako.
Now, for her birthday... things would basically play out the same. I suspect I'd trigger a neutral end due to being too worried about her, but I'd intentionally steer the conversation away from friend zoning myself, she'd pick up on me seeing her that way (but the self-doubt would kick in). If I did trigger a bad end due to not taking her to the city (even if it was somewhere), I'd react a hell of a lot faster than Hisao did, and leave by at least the second time she told me to get out (at speeds that would make me regret not running with Emi), if not sooner... but I'd tell someone like Nurse, which is probably worse.
In the case of the neutral end, I'd probably never give up trying to force myself to confess to her, but I would never succeed, and I don't see a possibility for Hanako to feel the need to take drastic action. If she was attracted to me, though, Lilly and Akira would be frustrated to watch nothing happening. I suspect Akira would end up locking me in a room with Hanako and a box of condoms (nothing would happen, we'd both be too embarrassed). If a relationship did happen, Lilly would probably have to be the go-between to get things started.
And it'd be a horrible relationship in the long run. Remember the bit about feeding off of each other's anxieties.
In the case of the bad end, I could possibly do a stone cold sober, Kenji-free version of the Kenji end. (Read: intentional suicide.) Back at that point in my life, I considered it over less.
The Emi route... I would be physically attracted to Emi right away, in real life. I'd be PISSED at her for almost killing me, though, and the puppy dog eyes don't have much effect on me, but full puppy dog would get my attention. I probably wouldn't go for it with running, but I'd probably keep trying past the second day, just not pushing it, and I probably wouldn't make it far... until Emi decides to get my ass into gear. (Ultimately, cycling's more my thing, for what it's worth.) I would consider her out of my league, but I'll note that the thing about Hisao pushing it was more about his mindset, not about Emi's. I could actually see Emi seeing something in me, and deciding to keep at it. I would be annoyed by her, but at the same time attracted to her. My fear of rejection wouldn't come into play, given how... forward... Emi was in the VN. (Well, it'd make me as darty as Hanako around her, and she'd have to take even more initiative than she did on the rooftop in the VN, but it'd still happen.)
That route would actually work a lot like it did in Hisao's route. I probably wouldn't have agreed to the anal, though.
I'd end up on the good route via Meiko... but it wouldn't last, we wouldn't have enough in common.