I run full speed towards them with my head turned back towards the court. At 6' 5"/250+, they get the message.
First time, I politely TELL them they need to be outside the 3-pt line or completely off the neutral zone (if there is one) on the end line. That doesn't work, I'm going to game mgmt or the cheer coach. If that doesn't get the job done, I employ the tactic in the first sentence of this post.