Oooh, I LOVE the clock idea

I gave my DS2 (who is 2 1/2) a Fisher Price Ocean Wonders Aquarium cot toy that lights up and has music and bubbles. I told him it is a special toy just for bedtime and he is allowed to press the button if he wakes up too early. I told him he is not allowed to get up or call out until he hears that mummy or daddy is up, but he can play with the toy while he waits. This has worked fantastically, he presses the button to play the music and watches the bubbles and lights, then falls back asleep.

Good luck