Michael,
If you are worried you may mess up the foam you can always buy a spare foam from John or just go and buy a set of those foam Yoga blocks that are 6" x9" and 4" thick with the same type of foam used in the rinehart 18-1 targets..That's what they feel like to me anyway.....
Just cut with a bandsaw,hacksaw,mitersaw or whatever you have and shape it with a bench sander or rasp to fit the quiver hood..They make a leather goop or plumbers goop that will hold the foam in place ... You can get 2 blocks for under $10.00 for the pair if you shop around for them and can make about 15 to 20 hood foam replacements... Just search "Yoga block"....
Now you can have a 5 arrow quiver and have your piggy backer as well...