Custom Context

I installed custom context and played around with it quite a bit. I can’t find out how to block an extension from dialing another extension. I created to contexts, and created to extention groups, 300-305 and 400-405. I want 300 to be able to call 301-304, but not able to call 400-405. Same goes with teh 400-405 group.

How can I set up custom context to only allow certian extension dialing?