Well, you can go two ways from here; One, you can get sneakier and sneakier, piling up lie after lie. Don't worry though, you'll never get caught or even get stressed out that you will.
The other method is a bit harder. Talk with your parents. They're your parents. If you believe that they will throw you out over this, then I think that crossdressing is the least of your worries. Approach your mother first. First, because she is a mom. Moms protect their children at all costs - sacrificing all. She is also a woman, very perceptive, and probably already knows.
Actually, I am getting ahead of myself a bit. The first person you need to talk to is yourself. Ask yourself where you really want to go with this. Why do you do it? If you stopped, could you live with yourself? Is it just the clothes, or is there more that you want?
Once you have these questions answered (which may take a it more than 15 minutes or so
), you will be able to talk to your parents and have better answers than shrugs and "I dunno."
Kathi