Ah Todd. 
Wouldn’t it be more fun to try an place a figure and have it jump right up and out of the car, or off the platform? 
Or, maybe, when you go to remove the figure, the figure comes up in your hand, but its feet stay firmly planted where they were.
Sounds more diabolical (and so does your image) than fun!
This past weekend, SVGRS set up its modules at RailFair 39 at Placer County Fairground. I put sheet metal bases on about half a dozen figures, and between ceramic magnets and magnetic picture holders, I was able to mount figures in freight cars, on a bench, and in a grassy field. Looked good and they were all pretty stable.
I’m out of space for photos on this board and too cheap to buy more space. So no pix. Sorry! This has worked really well. I’ve substitued 2 part expoxy for the Goo. I just make a small puddle with two dabs of expoy, mix them together, then put a small amount on each foot. Then let it set up!
A permanent solution for temporary placement of figures, with no damage to the place where the figure is to set.
One solution that I’ve had allows figures to stand in the outdoor sections of the layout is to (when possible, depending on the figure) drill a 1/16th hole up through the bottom of the feet (shoe) about 3/8 - 1/2 into the leg and insert a 1/16 x 2 inch brass wire into the leg with 1 1/2 below the bottom of the shoe.
Anchor that with a dab of CA and shove it into the dirt. or drill a 1/16 hole in a platform or whatever and they stand there right nicely and can be moved as needed…
If you drill carefully and not too much anesthetic is needed… (http://forums.mylargescale.com/images/smilies/cheesy.gif)(http://forums.mylargescale.com/images/smilies/cool.gif)(http://forums.mylargescale.com/images/smilies/rolleyes.gif)
I use Stan’s method where I want to be able to move figures around on the ground or bring them in to protect them from exposure to the elements.
For semi permanent fixing, say loco crews or passengers, I use a clear silicon based adhesive (in the UK it is known as “Seriously Strong Glue” by Evode). It easy to remove from surfaces without removing paint or leaving any residue. I never use super glues for this purpose for that reason and its lack of flexibility.
The magnet idea sounds interesting but perhaps a little over-engineered unless you want to quickly re-position the same figure in multiple places again and again . Max.