A.S.
I once read some advice on a forum and have never seen mentioned again which either means it won't work or that it is a brilliant and innovative idea. :)
It basically involves "conditioning" your son to wake up to music. The first day start the music fifteen minutes before he normally wakes up. Each following day push the music back 15 minutes later. (In your case: Day one: 4:45, Day two: 5:00, Day three: 5:15, etc.) Keep this up until you reach the desired time. It might be helpful to have a CD player you could pre-program. Hmmm...
I wonder if it really would work?! Good luck. I miss my sleep too. :)