Depends on how much you are faking it. Do you want the relationship to last? Or is it just a passing relationship?
If it's a short period relationship I think you can fake all the way at some point to will get busted.... Unless you have a multiple personalities disorder.
But if you are looking for a long term relationship I believe faking it won't work - or it depends the thing you faked; how important is that thing you faked to the person you are trying to impress.