My vet gave me some wormer for my feral, that I added to his food, based on what I told him about the age/weight of the cat, but even that is not ideal as there are so many kinds of worms. I would not use OTC stuff if at all possible.
Look for a local non-profit, private cat rescue group in your area and ask them if they would give you some Strongid T for a small donation. 1cc for an adult cat (liquid) gently squirted into the side of his mouth or mixed with food, once, and then 1 cc again 2 weeks later is standard practice. It doesn't taste bad, so you *might* be able to mix it in his food.