Here is a little setup that I use for balancing my grinding wheels. The stand is from my model airplane tools.
It is a prop balancer from DuBro. I have added some shafting, bushings, and a pair of cones for larger wheels.
Once I have the wheel fitted up to one of the arbors, I spin it and find the heavy area. Opposite that I will paint on the side of the wheel some Lacquer left over from my kitchen cabinet refinishing project. Let that dry and test again. Keep that up until the heavy spot is gone. Wait at least 24 hours for the Lacquer to harden and give her a go on the grinder. Works pretty good.
Another thing that I have found helps on most of my grinders is to eliminate the supplied washers and make a composite bushing/washer as shown in the last few pictures. It has improved the runout/balance on each wheel that I have used it on.