I'm at work atm, but (from memory) one of the 4 buttons in the middle of the window...i think it's configure...should open up another window which will have a "+" and "-" underneath 2 adjacent windows. Click on the left "+" sign then click on "assign keystroke" or something like that. Then hit "ok" or what ever closes that window.

In the window to the right, click on the "+" under that window. A menu with several options should come up which include assigning a keystroke to broadcasting.

Assign your keystroke then close that window and click OK and you should be Gtg.

I'm sorry if this is very crude, but I'm going from memory. Set mine up a while ago. When I get home I'll update this if you need me too. Just wanted to post something to get you going in the right direction.