Hyke, you could douse the plants in a solution prepared from those E-cig nicotine refills, that should effectively exterminate the lice. Assuming the plants are not intended for eating.
Good tip with the comfrey, lutra, your right though, that stuff fucking stinks like ten tons of arse holes. I use the root of the plant sometimes as an add-on to my antiinflammatory NSAID spray, morphine, oxy and steroid shots that I take for my squirrely knee and hip joints/bursitis, although it can only be used externally, due to the presence of hepatotoxic pyrrolizidine alkaloids, sort-of related to the liver-destroying nastiness found in ragwort and the groundsels. Nasty shit, if consumed they can fuck up the heart, lungs, kidneys, liver, cause cancer by buggering up DNA and worse besides, although absorbed very slightly through the skin, its only after the N-oxides of the toxic principles undergo toxification within the GI tract that they become toxic, so topical use of comfrey and the like should prove to be nontoxic.
Currently thinking 'jam filled cookies, yum!'