What I have done is the past is add organic catnip to their food- this gives them fiber they need to push the worms out of their system. An elderly vet who had a passion for ferals is the one who told me this way and he said he would not recommend it for domestic cats because it creates finicky eaters, however in ferals this is never a problem.
You need to add it to the food after it has been dried and crushed- it just pushes the food through the system- again this process does NOT work on indoor/outdoor cats, strictly on feral colony cats where putting wormer into the food is prohibitively expensive not to mention risky because you never know who gets what dose- don't use this method with your inside cats or you may find yourself with a cat that will not eat unless catnip is in their food- and talk about prohibitively expensive
Ok. I have inside only cats, and outside only cats. I can easily catch and treat 2 of the outside cats, but the rest are adopted ferals, so the catnip idea is a good one for them if needed.
I will be sure to pick some catnip and dry it so I can mix it in their food sometimes to help keep them worm free.
I have plenty of catnip growing in the yard all summer! But don't want to hook the inside cats on anything unnecessary. (I have only given them the catnip a few times.)
just thought i'd add my experiences to this thread
i've managed to worm 4 of the 5-6 cats in our area by feeding pieces of chicken with small pieces of the worming pill inside them. it's a long tedious process and the cats do have to at least be used to your prescence. We're lucky because we have large sliding glass doors and the food is left outside the door so they have to come up to the glass to eat and it's easy for me to just slip a piece into the feeding bowl if i hide behind the curtain and just stick my fingers out... there was one who was particularly difficult to worm because he was much much more weary of people than the others... But i guess your cats might be even more feral than these ones...
as for the weightill ratio i just have to make an educated guess based on the weights they were when they went in for neutering... and on similar sizes... i must try this organic cat nip thing anyway...