Not even remotely possible. Somewhere hard written into the system, DPIM's are not allowed access to trunks under any circumstance.
I had a customer who simply wanted a door phone to call external for emergencies, we tried every combination possible; forward to virtual, then to another virtual then to a mailbox forwarded out, could not trick it no matter what. It appears once the system see's the DPIM is involved in the call it just hangs up... no warning, no error at all.