Encrypting parts of a cyclone II FPGA

Hi!

I'm currently working on a project with Quartus II 11.1sp2. The FPGA I use is a Cyclone II EP2C5T144C8.

I wonder if it is possible to encrypt partially the FPGA chip in order to protect IPs and the behavior of the board I'm working on. I want to let a restricted zone reachable by a user where he could add his logic.

Thanks for help,

Florian