That's a great idea! If you can't change the behaviour, make adjustments to make it work.

Well last night he was pretty wrecked after a big day out, so he slept quite well, when I heard him get up this morning it was 7am (a time I have no problem with), but we have told him to stay in bed until 'the sun comes up' on his gro clock. So I go up and put him back to bed calmly and without saying a word. He stayed there till it was time to get up, came to our room and said 'mummy the suns up'.
So we had a pretty good night, however he still doesn't get his football and face book back because he got up before he was due to - he was a bit upset about that, but not enough for it to be a deterrent.

I still think the sensor on the door and just putting him straight back to bed will be our best option. Eventually he will give up, I hope!! Luckily he has no toys in his bedroom, so he has to walk out to get a book or something to play with.