M900 and M70 send DTMF by one key press

In an other Thread i mentioned that our doors are connected to the PBX. If anyone rings the bell on a door, the phones of some user become a call and can open the door after hook up with a specific code (eg: #61). This code is send as DTMF to the door.

We also have many Snom D385 and i use the key for "Answering machine" to send this 3 keys (#,6,1) to the door, means the User hook up the phone, press one key and the door will be open.

How can i achieve this on a DECT M70?

I tried to use the Emergency Key for that, but in the M900 base i can't enter my code, it must be a number only, i guess.

Regards