It took about an hour to magnetize 35 miniatures. To keep the magnets level with the bottom edge of the minis' bases (this is very important to get the strongest grip), I pressed them into a blob of green stuff and then smoothed them off by pressing the miniature down on my desk until everything was even. Here's what it looks like:
The blobs are up against one edge of the base to form a stronger bond between the green stuff and the base. That puts the bond on at least two planes instead of just one.
Before I zeroed in on green stuff, I tried gluing the magnets on with JB Qwik. It was a fascinating failure. There's something ferrous in JB Qwik that causes it to flow up the sides and over the top of each magnet, encasing it in a perfect sphere of epoxy. This wasn't good for sticking models to the sides of a desk, but it was so interesting that I dropped several magnets into the puddle of epoxy just to watch the process. Then I fished them out, cut away the JB Qwik and switched to green stuff.