In fact, Campbell explains that all the Jets have to do is tell McGroarty he'll have a role and invite him to training camp. That way, if he has the caliber to play in the top-6, he'll have proven his worth to the coaching staff and if he doesn't, he'll lose his leverage.
If he doesn't play like a top-6 caliber guy at camp, other teams won't want to trade for him by promising him a role on their top-6, after all.