Dialing number with pause

I am trying to get a configuration that dials a number, a pause, then another number and pound thruhg chan_mobile.

I have a custom trunk that dials out through chan_mobile that works ok, but I want to dial something like this

wait #

I tried to add w, and p to the dial string but it does not work. I need to create a custom context to this that dials the fixed number and when answered, dials the digits of the dialed number.

¿How can I add this to freepbx?