Collect bikes of all the same color. Then it will be less apparent to the casual observer how many you have.

I find that being seen bringing a new one onto the property is the problem. Once its there, it seems pretty benign. Therefore, avoid being seen bringing them in. Nightime, storage at work, hiding them in the basement, and off-site storage are all worth considering.

We all know there is a slippery slope between a pile of parts and an actual bike. Legally speaking a bike is complete. I would not suggest you lie, but I do suggest you look with clear eyes at how many "complete" bikes you own. I own just one bike, for example.

jim