Picking up a Zap channel and leaving it off-hook?

Hello, I’ve got a rather unique situation where I have a predictive dialer that talks to its agents over analogue lines. Currently, to log on, the agents simply plug in their analogue phone, and lift the handset. There’s no dialtone, and when calls come in the dialer passes them to the agent. I’d like to replace these analogue phones with IP phones that so something like this:

  1. Agent presses a pre-configured button the phone (dials 101 for example)
  2. Asterisk opens ZAP/1 and bridges it with the agent, despite there being no dial tone. Zap/1 would be connected to the same line the dialer uses to direct calls to this specific agent.

Another scenario I’m looking at would be one that uses an FXO/SIP gateway (a Grandstream GXW series or something) where:

  1. Agent dials 101 as per above.
  2. Asterisk dials SIP/101 (a sip channel on the fxo gateway)
  3. The gateway opens FXO port 1, and bridges it with the sip port, Asterisk bridges the call from the agent to the SIP device.

Does this make any sense? Any help would be appreciated.