I came across with a similar problem. There is no (programmable, at least) solution available at the moment as far as I know. But we solved it.
Now, please do not laugh, I am super serious.
What we did: instructed agents to press any number on the dial pad before hitting the transfer softkey. The caller party hears a beep which is actually the DTMF tone generated by the agent when pressing that number...
Well, our customer is happy with this solution, you might also give it a try.