Possible new feature - restricting the forwarding of extensi

Every company I have worked for has prohibited the ability of forwarding my desk phone to an external telephone number so its obviously a feature that gets used.

I have chacked the call forward routines in freepdx to add in a block to numbers starting with a 9 but I was wondering if there was a better way of doing this so we have a setable feature per extension or for the whole system to allow/deny forward to external numbers.

has anyone looked at this at all??