As a non-Muslim in a Muslim family, I don't blame your decision and don't think you're doing anything wrong. If you were trying to call yourself a Muslim but refused to fast, I'd see an issue but it's your issue to address, no one else's. You're not practicing the religion, so it hardly matters. Just don't get caught or you're screwed.
Honestly, I see it the same way I see having been forced to go to church as a kid. I'm sitting there to pass the time and because I have no other choice, not because I'm actually praying, paying attention or reading the Bible etc. And when you finally live alone, you won't have to pretend anymore.