I am just a lowly med student, but I too am a night person, and I too am finding that my natural sleep desires are incompatible with med school. Some things that I am finding helpful:
1. Make yourself wake up on the weekends / or days off. It sounds like horrible torture, but by forcing yourself to stay in the same schedule, it makes it a bit easier.
2. I avoid caffeine after about 12:00 noon. For some reason, once I eliminated caffeine in the afternoon, it made it easier for me to go to bed later - not sure if caffeine just breaks down super slowly in me or what.
3. A bit of light exercise in the afternoon (I hate excercise too, so I have to disguise it in the form of a game of racquetball or a jog on the treadmill while watching TV).
4. Set your sleep environment up so you get REALLY good sleep when you do sleep. Make the room very dark. Get earplugs so it is very quiet. Don't do anything in bed but sleep (or sex I guess if you are the sort that is getting some). No lounging in bed, no TV in bed - get yourself to mentally associate the bed with sleep.
5. No high intensity mental activity for half an hour before bed. In fact - try to avoid even something like TV or the Internet for half an hour before bed. For some reason, this worked for me in a big way. I just do a bit of recreational reading, or something brainless. Helps me slow down and mentally prepare for sleep.
Good luck! I don't even need an alarm clock now to get up at 7:30 (which of course is not 4:30...but I don't have to get up that early yet). I was used to waking up at 11-12 for many years before med school, so this has been quite a shift.