Just did it on mine to be sure, works fine. These are the conditions:
1. Must already be doing a live silent monitor or agent help call (you don't mention this, but I assume you are)
2. while you're listening, press SPCL and dial 387 (ASSUMING THAT'S STILL THE CODE ON YOUR SYSTEM)
3. Display should say CALL STOLEN, and it's all yours.
If you're not already doing silent monitor, be aware that you must be the supervisor of a hunt group the other person belongs to (though you can then also monitor non-HG calls)