People are either going to follow objectives or not. Simply tell them you get roughly 50% more XP for do anything at an objective and they will soon flock to it.
I'd just prefer to solve the underlying problem, since few pugs set objectives a request command feature which if the leader didn't do a command in lets say 1 min. would then transfer the squad lead to you.(the requester) essentially what battlefield has
If you dont play the points and lose you get hardly any XP. Even with a fair number of kills you may earn less than 2k req when your team loses. Free players will get one third of that. I got a feeling they will soon learn. If anything i can see them getting salty at the premium players who dont go for points and end up getting three times more xp than them for doing nothing. I think this is more of a problem with the way matches are set up, wins/losses are handeled and how players are rewarded with req than the attitudes of players. I mean, khorn cares not from where the blood flows.