I searched around google for others having this problem, but found no solutions. Than I found this thing:
http://www.softpedia.com/progDownload/MultiMonitor-Cursor-Lock-Download-93070.html
Pretty easy to setup, the demigod executable is in some path like this:
program files/stardock games/demigod/bin/demigod.exe
enjoy, oh also stardock if you are listening please just add this obvious fix to the game, surely your developers are using dual monitors to program (I use 3 when I do)