I didn't say cut it out -- just ramp down. Lower quantity, and do alcohol/coke in "boring" ways, like medicine, vs. associating them with fun stuff. Or, replace with somewhat less destructive drugs (alcohol abuse is way worse than coke, IMO, except that coke is illegal)
Do visa waiver for 3 months, and work for cash/informally, or as a contractor. I'm sure you can figure out a way to stay past that. (if a company really likes you, they could help) Or, Vancouver, BC is probably adequate. If you're otherwise going to kill yourself, I don't think pushing the limits on a visa is a big deal.
The other thing would be get into a US university. If you can't get into a top-tier school, go to an ok school in an interesting location (I'm not sure how they do foreign students, but even something like Foothill College in the Bay Area would get you near a bunch of startups).
It's not that easy. Tried to quit before and I can't last more than 48 hours without hallucinating.
"SF or NYC if you want to be a SW engineer"
Would love to move to SF, but like you guessed I'm in the UK (London). Getting a visa is very difficult.