I see what he's saying...just keep a few of the sausages around in order to maintain the illusion that is what he's eating...while sneaking mice into the house to actually feed to the snake...
I do think that you'll get caught eventually...its only a matter of time! I still think that taking the initiative to do things around the house, clean your room w/o her asking, and things like that, will show her that you are making an effort to be responsible and she may be more willing to be a little more open-minded about getting a snake that eats mice. She probably figures if you can't even handle doing basic chores, keeping your room clean, etc, how is adding a live animal to the picture going to help things?
Just my .02....