Shameless plug: You may be interested in the TvGameLauncher tool I wrote for exactly this purpose (switching primary displays for playing games). It can also switch to HDMI audio and prevent the screensaver from popping up while you're playing (without disabling it). It even supports the Steam protocol (Steam://) so you don't have to use the pause trick. It doesn't support disabling your other monitors though, but I'll add that to my todo list (I have some other cool features coming up like automatic TV shortcut generation).