How do i manage to make it to this party...?

My boyfriend is going to have a party this weekend with his hockey teammates, as kind of a farewell thing, because we are seniors and it was their last year playing together. Of course there will be drinking and everything, But, honestlly, it will be supervised, both his mother and his father will be there, they take everyones keys and hide them, no one can get out of the house once they are there, and no one can leave the house the next day unless they believe that we are sober enough. The problem is, my mother. This part was supposed to be last weekend, so she allowed me to stay the night. How can I convince her to let me stay the night this time? I can't lie and say that I'll be at a girl friend's house because it'll be two weekends in a row that I am sleeping over somewhere. And she is a phsyco mom who is afraid of spending the night alone in the house. Is there anything I can do to convince her to let me go, or what is the best way to kiss up to her and get on her good side so that I can go?