I guess they're not as hungry as I was hoping: even with the garlic I got little interest in the Jungle food. Oh well, they'll get there eventually.
I put the sick on in a breeder box for a couple hours to observe his poop. It seemed pretty normal to me: 0.75-1.0cm long, greenish-brown coloration.
I've now dosed the tank with the Parasite Guard I mentioned earlier (including letting one of the tablets dissolve in the breeder box to give him a little-bit stronger dose before releasing him again).
Now I guess it's just a wait-and-see until I get Charlie's meds.