You can't have more than one DTMF_ID associated with an individual Exchange alias in Unity 2.4.x You need to use call handlers to manage this sort of thing.
It sounds like you need to somehow work around the limitation that Call Handler greetings can't be recorded via the subscriber conversation. The subscriber doesn't need to be physically present, you could have him record the handler greeting into his alternate greeting, then copy and paste the WAV file to the call handler. You could have him make a WAV file and send it to you. If coordinated correctly, you could use the SA to dial whatever phone he's sitting at for the TRaP connection, or conference him in. I admit none of these are as slick as using the TUI, but we've addressed that in 3.0.
Unity 3.0 has support for multiple extension ID's for subscribers.
Scott Morgan
Cisco Systems TAC