Here are some photos of my new basing that I am using. I have picked up some buttons from an online dealer on the cheap. What I did was trim the metal bases to fit in to the recess of the button, then glued them in. Once dried I filled in around the metal base with Durham's putty. I mixed it thin and piped it on with a plastic bag with a tiny hole in the corner. Then I took the bottom of the base and hit it with my sander. The bottom of the buttons are slightly rounded, so I wanted to knock that down a bit.
Photos 1 and 2 are the same batch of minis, and photos 3 and 4 are another batch. I did 3, and 4 first, then moved to 1, and 2.
Well the next step is to clean up the water putty, and prime them for paint. I was going to use gesso but I think there are to many for that.