that's why you aren't running it.
hell, i'm ready to include trainer rides - since the structure they bring gets more people working-out, which means more people at short-track displaying their new power curve.
i'd even count running - but not swimming. nfw.
I think most "cyclists" don't want to mix up running or other activities/sports in this thing. That's OK.
If the main idea of this contest is to promote riding, and specifically build a base during the winter so we start as best as we can the next season, riding a bike on a trainer should count. Riding on a trainer is still pedaling a bike, and is usually hard riding too. If the idea of this contest is to see who's the most macho and gets outside more in the coldest/shittiest days, etc., then don't focus on the hours pedaling and structure the points to reward those things.