Become a morning person (oddly enough, I'm typing this at 12:45 am... but I'm also unemployed right now). Use brainwave entrainment technologies and meditation to get yourself to sleep in the evening, because you probably haven't had a habit of going to bed before midnight since grade school. Most people need less sleep if they go to bed and rise early, so if you're asleep by 10, you can get up around 4:30 easily.
Why are traditional jobs scheduled between 9 and 5? Because despite claims to the contrary, the majority of people are naturally "morning people" and most productive early in the day. The boss wants the workers' best hours, and most people get up around 8. If you get up much earlier, though, you can use your early morning hours for exercise and side projects. This will be a lot more effective than trying to use your burned-out evening hours, and unlike quitting your job, it won't hurt your career. You'll be pretty tired by 5pm, but the effect that this will have on your performance or career is negligible.
The only downside of this is the effect it will have on your social life, but that's a lot smaller than you think. You'll still be able to manage the occasional late-night party or code-fest, but you'll find your 2am IM chats no longer occur. Socially, you'll be focusing on quality rather than quantity, which is not necessarily a bad thing.
I had a similar experience to yours in previous jobs. I wish I had taken the advice I'm giving you now, and as soon as I'm in a structured work environment again, I'm going to switch to the early-morning rhythm.