The product that Keith is talking about is named blue tack from bostik, I think. It's always used to block securely the wooden base of the figure for transporting them in various shows and it is enough strong to block small figures in the painting wooden base but for larger I think it could be a little dangerous.
I make always the same hole of the figure on the wooden base used for holding the figure during the paintig session.The pins, that are quite always from paper clip (consider that I paint quite excusively 54mm figures), are totally inside the hole I have drilled in one of the discarded wooden bases that I have. In fact I use a specific wooden base for the specific scale of the figure, higher for the 90mm and lower for the 54mm.
Marco