Re: Ideas for a cheesy birthday party...
Why don't u ask one of u'r friends, to take him out for few hours. May be for a movie/a game of tennis/for a walk. This will give u some time. Cauz i think as long as he'll be in the house, it wont be a surprise anymore.
Decoration part you hve to do on friday and close that room. Finish of cooking on friday as much as u can. Cooking on Saturday can be dangerous. But yea u can still cook some thing.
Other thing u can do, if he is not willing to go out with friends, is to ask 1-2 friends to come before time and start chatting to him. Just to distract
him for some time. Than use back door, and let every one come in from there. Plus food and fresh cake etc etc.