Thank you for helping this feral cat. He looks well fed and healthy in your pictures, apart from his skin lesion.
I am a veterinarian and will do my best to help. I am sorry you have waited so long for an expert. I just came online today and saw your question.
This does not look like mange to me. Mange is caused by a parasitic mite, is fairly rare in cats, and usually affects more than just one spot on the body.
It could be ringworm
, a fungal skin infection, which is more common in cats than mange.
It could also be a skin infection, from a fight/bite wound from another cat ( he looks like a male cat, and if he is not neutered, cat fights would be common for him over territory and females). Or it could be from scratching at his ear, if he has an ear infection
, or ear mites.
If you can't handle him and apply any medication to him, it will be very difficult to treat him. If it is from ear mites, and his scratching at his ears and face from the mites, you could try to get .1 cc ( 1/10 of 1 cc, about 1 drop) of Ivomec (ivermectin) into him by hiding it in food, but it is very bitter and he might not take it. It only needs to be given 2 to 3 times, at weekly intervals to treat ear mites.
If it is a skin infection or ringworm, the best treatment is applying anti biotic, anti inflammatory and/or anti fungal ointment to the area, and it does not sound like he will allow that.
Let me know what else I can answer or help with.