Just scale the roulette bonus dependent on how many people queue. Something like 2 people queuing gets full bonus, but 3 gets 66% and 4 gets 33%. Take away adventurer in need outside of solo too.

I always thought that an mmo penalising you for wanting to do something as aa social group was odd, but I can understand the reason. However, leveling a tank at the moment I would love to be able to give my FC mates quick queues.