In my experience, the best way to sell a miniatures game, is to play it. We (my co-workers and I) used to play Warmachine in our hobby shop, and within a month we had four new players who within a month each dragged a couple friends into the game. Get a decent board with terrain (fully painted and with real miniature trees and buildings- not just felt) and a couple painted forces (not too hard with 6 figures to a side) and play the game where other customers can see. It might be a good idea to keep the rulebook open to a character's page, even if you don't need to use it, as it lets them see how nice the book looks inside. When people ask, give a basic overview of the game, and let them watch. Not everybody will bite, but once you explain that a force only costs on average $60-80 (as opposed to $400-500 for a Games Workshop army) people will start to buy in. Play 100 / 150 / 200 level games with them as they build up their forces. Don't force painting on people, as some people have no desire to paint minis (part of why MageKnight did so well).
Once you have a bit of a player base, schedule regular gaming nights and maybe even run a tournament. With enough people, a $2 - 4 buy in allows you to buy a miniature or two as a prize.
Yes, it's a straight up sales pitch, but I promise you- it works.