As it stands now, the only thing you could really do is establish a separate iTunes library for the content that you don't want accessible on your Apple TV. The easiest way to do this is to launch iTunes while holding down the Option key. It will present you with this ....
1. Create a new iTunes Library.
2. Hold down the option key whenever you want to launch iTunes and switch libraries.
3. I'm not sure if the Apple TV links to a
specific iTunes library or if it simply links to the library that iTunes
most recently opened on the machine. (You'll have to try this out yourself since I don't have an Apple TV yet.)
This ought to point you in the right direction. Good luck!
OAW