I think they would be fine, honestly. I've talked to Dr. Robert Mason about this before. He's a professor of zoology, specifically heavily involved in studying garter snakes. He has his own lab and everything at OSU. He says it's perfectly safe to feed your garter snakes WC frogs even if they have parasites, provided you freeze them at 0 degrees F or colder, for at least 60 days. I have a dedicated full size freezer, mainly for vacuum sealed meat. It fluctuates between -3 and about +3 degrees F. I think that would work just fine.