this is not really a "vicidial" concept. more of an asterisk/php concept (or perhaps even pure asterisk, but that may be tricky).
the goal is to play a recording in a meetme room/conference based on some form of input on the user screen. that's not actually difficult for an asterisk professional. then comes the "what to play" and "how to initiate" (with authentication). that's a php/mysql bit which would probably be best done within vicidial, perhaps in an iframe within the script for ease of creation (no editing of the vicidial.php agent page itself).
alternately, it could be initiated with hotkeys, but that's debatable.
I'm sure if you paid The Vicidial Group, they could do it quickest ... even though they are expensive, it would probably be fairly easy to accomplish simply because they know their way around vicidial's code and ARE asterisk professionals (nice combo LOL)