I do'nt know, but WHY would they want to do this anyway? They don't need MBs to take advantage of FP+, they can just use their tickets to enter. Since they aren't staying onsite (assumption based on them possibly needing someone else's MBs instead of getting their own) they won't be able to charge to them. There's just no point.
Assuming you're going back in the future, just put them away in your travel drawer (if you have one...we keep Disney stuff, passports, etc etc in a big drawer) and pull them out for the next trip.