So let me get this straight.. You want for him to sleep between 8:15pm or so to around 7-8 am in the morning? Do you realize that's almost 12 hours?
I realize that at times children will sleep long like that. They will go through growth spurts where more sleep is needed. But the older they get the less they need for quite a long while. Interestingly enough, 12 year olds need nearly that much sleep per day.
I think you will need to decide what personal time you value most. Do you most want time to yourself in the afternoon or evening? And, is sleeping in important to you or do you like to get up and enter your own day slower without a child needing so much right off?
You will not make this child sleep 12 hours per night if he doesn't need it.
However, if you really want to try and make that happen, run him ragged during the day. Take him to the park for hours and hours per day and skip the naps too. He'll sleep longer. Sometimes this is ok if you just need more personal time. No one can fault you for that. But it's an exhausting thing to do and really can't be done everyday.