I presently use the default music on hold for the queues with a join announcement. However I’m looking for a wav file that has music and prompts in between stating thank you for your patience, please continue to hold etc. to play instead of the default music on hold.
Do you specifically want the agent to be able to interrupt a comfort message, otherwise the run time merging done by the queue application should work.
Provided the licence on the music allows derivative works, it is fairly easy to create a merged file yourself using sox or Audacity.