If I want to test this on only 1 of my 4 cards in my 280x rig, is that possible?
Yep, and you can add licenses to the rest of your cards later if you like.
cgminer lets me specify devices by using -d switch ; does your software let me specify which device to use and leave the rest for scrypt or whatever?
As of now, it won't let you choose which card to mine on, though it will leave others for whatever you want.