Assuming they would work, where can i put tens electrodes to help with opiate-induced constipation? which nerves stimulate peristalsis?

Physiology, Marilyn: You've got 2 things wrong: Gut muscle is smooth not striated muscle, & peristalsis is intrinsic to the gut, maintained by myenteric plexuses throughout the intestinal walls. Sympathetic NS stimulates it & parasympathetic NS inhibits it. There isn't any one nerve that controls peristalsis. For more information consult any basic physiology textbook.