Try to put the food for him at the same place each time. Is he coming on a regular schedule each night? If he does that it means he is hungry that time of the day so you need to take advantage of it.
Put the trap right near the spot where he usually eats. Cover it with a sheet or towel so he can get used to the shape and smells. When the right timing has come (as soon as possible considering the facts) set a
very small (tip of a tsp) amount of food where he will lay the first step in the cage, straight on the ground between the bars of the cage. Then put a fairly big amount under the cage, in the very back - so he walks the length where the trap can close. It is best to put the food straight on the ground at the back of the cage and then lay the trap straight on it (the food will slide up through the thin bars) because if you set a bowl with food there he might get hurt while trapped inside - he won't like it.
The reason you have to put a towel on the trap is to make it look like a tunnel - at the end of which there is the food.
Use canned food - TNR operations also suggest mackerel - having a strong smell to it. I had success with plain canned food -since I had to make sure the cats were extremely hungry.
Keep the cage covered to make it as less stressful as possible for him. The more he is able to see he cannot get outside the more he will hurt himself against the walls of the cage. The darkness provided by the towel or sheet will keep him calm.
Warn your neighbours not to make sudden noises; you could sit at a distance - where he could not see you to make sure no other animal is accidentally trapped and so that you can take him in as soon as he is gets in.
Let him covered overnight or until you can take him to the vet. Also make sure he isn't too hot or too cold.
I have set fans in the garage for the cats that are recovering in the cages after having been spayed /neutered. I have to change the newspapers from underneath the cages on a regualr basis since there is no other way for them to go potty. Also protect your car while you take him in - lay the cage in a card board box, lay newpapers because accidents may happen.
Best of luck and let us know how it goes
I can't forget to mention that is so nice of you to try and take him to the vet
