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You are correct that there is a good bet that your cat has a fungus...specifically ringworm. This could be potentially bad news in cats where there are multiple affected sites like this. If this were ringworm, at this stage, topical therapy alone would not suffice, even if your cat would accept treatment...at this point, he would need to be treated with the oral antifungal griseofulvin. Treating him twice a day every day, would clearly require a temporary life style change where he is kept indoors (perhaps in a garage) where he can be approached and consistently treated every day for 2-3 weeks.
Another possibility for your cat's distribution of skin lesions is mange, a mite parasite that burrows deep into the skin and leads to lesions similar to what you are describing for your kitty. This also would require treatment, but luckily can be treated in most cases with an injection every 2 weeks for 3 treatments.
Unfortunately, there is likely no way around this other than getting your kitty to the veterinarian. As far as catching him, most feed stores and farm equipment stores sell cat traps that you can leave food in to try to trap him so you can take him in. You can also simply try using a small kennel and leaving food in it (but in this case, you would have to watch it and shut the door once he is in).
Once at the vet, he should have a skin scraping to check for mange, as well as a fungal culture to check for ringworm, then treated accordingly.