I have a script that uses the "upload prompt" step. Some of the prompts it uploads are large and take a bit of time. Is it possible to play a wav whilst this transfer is going on?
I would suggest not putting "Music on Hold" in your thread subject then.
The answer is no unless you're real good with Java. You could create a seperate MoH stream on UCM, create a seperate set of CTI Ports for this application, and set these ports to that other stream; however, that may not be desirable depending on your environment. It certainly isn't very scalable.