If there was a way to join it to a jell of some sort, and just make your own apiguard mix, you would have to figure out a good mix per evaporation combination. I don't know how U would do that but I bet you could find it somewere on the net, to figure it out. mix it with pectin or some type of jelly mix perhaps. so the bees could cart it out.
the bees clean it out of the hive, but a cotton ball would be almost impossilbe for them to pull apart and remove, I would think, in api-guard its a jell so I would work with that make a cup of jello/pectin perhaps with 3 drops of thymol. test it and do a mite count. I would try it slowly at first and work up to a dosage that works for you. make it a bit weak so it could evap and dri out.pastey. hmm might try it myself.
Me thinks it would be a bit of work but in the long run way cheaper if it works for you.