I think you can use Cod liver oil, I don't know if you can put them on the bugs though. You might want to take them to the vet if they don't poop for while, it could be an impaction.
hmmm, my Alfie was treated for mild mouth rot 2 weeks ago & has only been eating for those 2 weeks (first force-feeding, now eating on his own) & hasn't pooped yet. Maybe I should take him back to the vet for a check-up & mention it to her