I would also go down the carrot and stick route.
"DN, see this grumpy face/red card/Fuck off sign on my door? If it's on, you are NOT to knock on my door. If you do, I will be grumpy and shout as I need 8 hours of sleep and go to bed MUCH later than you so I need to stay asleep. Otherwise I turn into a bear and GROOOWWWLL. (with actions if poss!) When this happy face/green card/come in dear sign is on my door, that means I'm up and happy to play. Let's practise" Make it into a game, he'll love it.
"Now, if you manage NOT to wake me up you get a smiley face sticker, and when you have (however many days you have left) stickers, then we will go to the shop together and I will buy you x. (small gift, sweets, whatever will work).
If you do wake me up I will turn into the bear with the sore head and GRROOWLL at you all day as I will be tired and grumpy. I won't have any energy to play. Do you want that? If you wait until the right sticker is on the door I will play with you. I don't believe you can do it - what do you think?"
He will respond - they all do. Combination of threats and bribery. Follow up your threat - if he wakes you every time he speaks to you GROWWL at him and look grumpy. Say "DN this is because you made me into the bear with the sore head. I'm grumpy because I'm tired. Do you like it?"
When he doesn't wake you up do massive over the top praise "I slept so well, I'm so happy. I'd love to play that boring game with you a million times. You're so clever and you've made me so happy. Well done!!!! Let's put your sticker up".
Worth a try!