Forbury LionYou can award them caps for appearances and make them wear them during the game.... or make the players repeatedly call out their numbers like they're playing kabadeSnowballmorganb
It might be a bit tricky to find 20+ different haircuts but are players allowed to wear wigs (or hats) on the pitch? You'd only need 11 and when someone is subbed off they could swap headgear like when a subbed captain hands over the armband. They could also sell replicas in the club shop.
They could wear coloured bathing caps. Excellent idea
Also they could have little cameras on top so we can see their view of the miss etc
And following in the footsteps of Inflatables Day and Portugal Day, we could have Hats Day where everyone in the crowd has to wear a hat.