i recon they should just do a skills weekend
anyone who wants to show up can, and they announce the team on the weekend.
40 yard dash, broad jump, vert leap, bench press, Oklahoma drills, passing competition (throwing at targets or buckets, what ever), could have OLmen push weighted dummies in a race, DL could do a shuttle drill where they have to go inside, outside and sack a dummy QB.
Im sure NFL people could come up with a range of skills competition and drills that can showcase every positions skill set and give them something to prove