Bill,
Here is something you may want to try out. Add some type of texture to the bottom of the trigger guard like skateboard tape or checkering. Now when the left hand is coming into the grip, "pinch and roll" it into position. Boy this would be a lot easier to describe with some video. The left index finger contacts the back of the trigger guard and touches the front of the middle finger of the right hand. The left hand is at a 45 degree angle to the right hand at this point. Now roll the hand up and point the left thumb at the target. The left hand in the final position is fully locked into both the underside of the trigger guard and the back of the hand has a full "meat" contact with the right hand. You should feel pressure on the index finger of the left hand being pinched in place.
Hmm, its late and I may have to rewrite this again for easier comprehension.
Best of luck and I will look at it again in the next day or so. :-)