Switch video game from iMac to external monitor?

[Tofray]

Can someone tell me if this is possible?

I'm ordering a new 27" iMac and plan to use my 22" Dell Monitor as an external monitor. I plan to mount the external monitor approx. 10 feet away from the iMac (using displayport to HDMI adapter). I want to have the option to play video games on the iMac monitor, then move the game to the external monitor exclusively when I want to change sitting positions. (External monitor is across room). Is it easy to just move the game to each monitor anytime I want, or do I have to install some other software program to make that happen?

Thanks for any help!