Why not set up a race limit registration system. When you register to fly a camp, you have to register what race/side you're gonna fly on, but have the registration server set up so that you can only register to fly for that race/side so long as the number of players registered for all races/sides are no more than say a difference of 2 from the largest populated to the smallest populated.
And since in most OP camps it's usually 2 sides anyway, have it so that if you want to fly Alliance or Coalition, and say Alliance has more players registered than Coalition, an Alliance pilot can't register to fly until such time as someone registers for Coalition, or they register to fly Coalition.