The only trick that works for me is to "fake" shoot at the target. That is, do everything the same up to the shot, but just hold the pin on the spot you want to hit - but do not shoot. Keep the pin on the spot. Just let down after holding on the spot. Do this instead of practice shooting for a few sessions and you might be surprised how well it works. This trains the brain not to fire your trigger finger when the pin gets close.
The other trick I use is to get within 5 yards of the target, and do not aim at anything but the center of the target. Do not pick a spot to shoot. Shoot several times at this close range and just focus on your release. This trains the brain to separate your trigger finger from your automatic brain response to release the trigger.