Just a little warning for you. Some people here think we shouldn't discuss stealth techniques here. Personally, I don't think it's rocket science and it really isn't too hard to figure out on either side (tapers or security).
Full (or nearly full) sized mics are going to be harder to hide, but just use your imagination. Try things out at home, and make sure you're comfortable before you go out.
Techniques will vary depending on the venue. I recorded a show last weekend and pretty much did everything in the open. Venue staff didn't care (even though there were no taping signs up).