CallBack Question

I have callback enabled, works just great. Except after the customer hits the callback number, it hangs up rather unceremoniously. As a result, our clients are calling back on their own accord.

I can’t make the appropriate changes listed below in the extensions file because freepbx writes over them. So does anyone know where I can put:

exten => return,1,Set(MSG=custom/call2back2)

Thanks a lot!!!