I would attach some pvc to the back of the snap, and sand the back of the pvc and the armor to give it a good hold. You could use goop, epoxy, or anything strong should do the job. I used goop and attached magnets to my armor.
Yes, attach the snap to a small piece of pvc or abs, lightly sand the two surfaces that will make contact (NO paint, oil or dust) Devcon makes several types of 2-part epoxy that work great. You can find it at OSH or Wally World.