You can try this method (it assumes you're right handed):
- Safety on
- Gun pointed in safe direction
- Remove magazine (if possible)
- Hold the slide FIRMLY in your left hand (a thin leather glove might help but it's not needed). The heel of your left hand should be on the left side of the rear of the slide with your fingers wrapped around the top. Just like you were going to rack the slide.
- Use your strong hand to SMACK the back of grip very hard. Withdraw your right hand about 12 to 18 inches from the rear of the grip and forcefully shove it forward, grabbing the grip of the gun while maintaining the firm grip over the slide with your left hand.
- It might take two or three attempts but that usually works.
Just make sure you hold on tight to the gun!