Using DISA from internal context

I want to let people making privat calls from there intern phones by using a pin. So I would like to use DISA from my intern extensions.
But DISA is only reachable from outbound routes.

Is there a way to use the grafik frontend from freepbx or do I have to edit the extensions_customs.conf by hand?

First I thougt I can use misc destination.

Thanks for help