I never had anything bad happen from simple manual stretches. I seriously doubt anyone can pull hard enough to do any damage without first causing pain which should be a clue that one should stop.
Since stretching is to be done flaccid it’s unlikely that the grip used would cause any damage. The best place to grip is the glans (head) using an overhand approach (thumb toward the body). Use powder, talc, a rubber/latex sheet, or piece of facial tissue (Kleenex) to improve the grip. Grasp the glans in the palm and close the fingers over it then lock the fingers with the thumb. The thumb should be at the sulcus (groove) where the glans and shaft meet. Use the triceps muscle to move your hand away from your body.
This grip avoids the main nerves on the shaft and compresses only the spongy glans. Since a stretch is going to last only about a minute there should be very little risk involved in compressing it.