Ondine,
Thank you for your suggestions! I do have a crate that I bought, and I can start feeding the ferals in the crate only. Obviously, I'll probably get one shot at this, in that I'll only pull the twine when Tipper is the one in there. If it doesn't work, I probably won't get a second...
I had some feral cats TNR'd a few years back, and have been feeding them since. Two of them fought and the following day, a "bubble" appeared under "Tipper's" neck. There is no way he will enter a trap again because he remembers the TNR. His energy level and appetite is the same as it was...