L.C.
Teach him the number 7.
Put a digital clock in his room where he can see it. Put tape over the minute numbers. Tape a large #7 above the clock. Tell him he wake up when the clock says 7.
The clock rules!
I did this with my children and it worked quite well -- especially when they were toddlers in big kid beds. If the clock doesn't say 7, you can't get up.
LBC