envoyohio, gave a very good description of the release.
The modern game requires bowlers to learn more than one release. If you read Ron Clifton's article on
http://www.bowl4fun.com about "The Dancing Fingers". It will explain different hand positions and what reactions they impart on the ball.
As far as spinning the ball and too much axis tilt, that is caused by the thumb leaving the ball a bit too early and the fingers spinning around the side of the ball as the pass the sliding foot.
To get more forward roll you will need to have your friend keep his thumb in the ball a little longer. The thumb should still clear the ball before the fingers.
As far as letting the ball turn your hand instead of your hand turn the ball. Put your fingers and thumb in the ball, and get in your starting position (you can do this at home you are not going to release the ball in this exercise).
Next I want you to place the weight of the ball in your opposite hand and let your index finger of your bowling hand (your hand still in the ball) point toward an immaginary target. Next let the weight of the ball roll back into the bowling hand with your index finger pointed at the target and fingers pointed toward the inside. Next let your thumb come out of the ball as you lift up on the ball and let it roll back into your non bowling hand and watch the ball rotate on it's own without you having to turn it. You can modify the rotation by pointing your ring finger toward the target this will give you an almost end over end rotation, or point your middle finger at your target giving you about 45 degrees of rotation, or spread your index finger and get 75+ degrees depending on your flexability and wrist strength.