How about a cell phone holder that clips on to his pants?  This would blend in the most.

 Or....I have seen strap on "pockets" that people can wear around their lower leg(s) to hide money while traveling. If there was a "pocket" that was big enough that might work. It’s not ideal... and would require long  pants.   ???

 Another idea is a small camera bag.  I’ve provided the school with  one just big enough for the shot plus supplies ( needle, alcohol swap etc..) There is also an area for a credit card size ID or picture.

 

 

Susan