This is a really simple thing to do. I picked it up from Les at awesomepaintjob.com
Basically it gives you a little more control of how you hold your miniature while painting and keeps your fingers away off your base.
1. You need the figure you are painting setup on the base as you want it and ready to prime.
2. Loctite Blue Tac or similar product ( the blue stuff you use to put posters up on the wall so they don't have holes in your dry wall)
3. A old dried out Games workshop paint pot
make a ball of blue tack
push the blue tack onto the top of the lid for the Games Workshop Paint Pot so that it covers the whole top and is smoothed around the edges (this keeps it from pulling off as easy when you take your model off.
Push your model
PUSHING ONLY ON the base firmly into the blue tac till you have it in the position you would like.
Prime Your model and your ready to paint.
If you would like to add some weight to the handle Les suggested filling the GW paint pots with sculpty clay. ( I haven't tried that yet.) Also if you want a bigger grip you can take two of the Games workshop pots and put the bottom to bottom and super glue them together that way you can grip it with your whole hand. If you get froggy you could even wrap the whole contraption in some foam tape. (ok maybe that could be going a little far.)