Bind internal extension to SIP trunk

Hi all

I have the following working scenario:

Remote pbx (epygi) registers on freepbx with extension xxx.
Remote pbx (epygi) forwards calls from landline to freepbx extension yyy.

I would like to know if I can set up a trunk on freepbx using internal extension zzz so it can forward calls from freepbx to remote pbx (epygi). The remote pbx (epygi) would register also on freepbx using extension zzz.

Cheers
MTV