Keynote with 3 screens

How do I make the presenter screen go on screen 2 and the display onto screen #3... So that my iMac is NOT being used, just the other two screens. This is necessary for me because the two external monitors are sent to a stage monitor and the projector... Currently we are mirroring the iMac's screen to screen 2... but it makes everything flash during the transition.

Basically, can I specify which screen the presenter and presentation images are displayed to? (When using a 3 monitor setup)

Thanks