The small shop I ride for is less than a year old, and is primarily freeride oriented. The owner doesn't have lots of bikes on the floor but moves a fair amount of special order Konas and Banshees. He uses a number of methods to market the scene. Here's a couple that seem to work for him (in stream of consciousness format, sorry):
First and foremost: Keep it real. He rides all the time, leads weekly urban rides out of his shop, takes groups on weekend trips to Snowshoe and Wintergreen (two nearby lift serviced mountains). He was active in creating and building our city sponsored bike park, and gets lots of business by talking to the kids out there. A few free t-shirts for the groms go a long way toward creating loyalty and additional business. Additionally, he has made the shop is a hangout of sorts, with couches, bike videos, Xbox, and lots of magazines to hang out and read. The kids love it, and the next thing you know, in come their parents to buy bikes too. But ultimately, if there's no scene, no one will want to get in on it.