To start it, make one big meetup that you think will draw people. Make it at an exciting place in the area, chose an interesting meetup topic, or plan a fun activity. An alternative if you're really desperate for people is to draw on the surrounding area by posting in more public places.

From there, all that has to happen is a successful Less Wrong meetup, using the strategies in the OP. That is usually enough to get some of the members to come back a few times, and if the meetups continue being interesting, new members will become regulars.