Rot the food, poison the T-Rex. Order whole cooked animals, cooked bones are horrible for animals because they don't bend like uncooked but rather...shatter. Creating lots of little potential daggers & knives to perforate the T-Rex's digestive tract. Also might be tougher to poop out. Poison, and internally wreck, the T-Rex.
Agitate the animal as much as possible & keep it alert. If able to time it right & the T-Rex never gets rest, it will eventually have to fall sometime out of sheer brain-dead exhaustion. As others have said, stab it in its guts with a poopy, poisoned knife.
Idk it would be difficult & arduous but I don't think it's impossible.