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.