Well, there is a pretty "unorthodox" strategy that you could use. I'm not even sure it's ethical to tell you this, but most new forums have only a couple of membersm, each of them having about 5 to 10 different users. They randomly log in each user, post/reply etc thus creating a pretty active forum. The others (the real users) are bound to join the discussions, out of interest...or whatever.
I've seen it done a million times, I'm sure it won't stop with you
With my club site, its always been a struggle. One thing that somewhat helped is a monthly newsletter emailed to everyone associated with the club urging them to participate in the forum, along with other valuable news items.
You could do that, but the most important thing is to get them there first, and do something to make them stay. And if you do as EagleImagery suggested, try not to sound too silly in that controversial topic