To shoot weak handed, you need to work on three different areas. Mechanical skill, manual dexterity, and grip strength.
Mechanical skill is the only area that needs to be practiced using the gun. Your brain and your strong hand both know how to grip the gun, control the trigger, and operate the other controls, but your weak hand does not. Like the above poster said, treat it like any other beginning student. Build a consistent grip, then work on trigger control, and finally add in the other aspects of gun handling, working from leather, reloading, clearing jams, etc.
Manual dexterity and grip strength can both be worked on without the gun. Try using your weak hand for everyday activities, like brushing your teeth. Pretty soon, you'll find yourself with a useful hand. For grip strength, I'd suggest one of the grippers with separate buttons for the individual fingers. That will help you avoid a problem I had, which was that although my thumb, index, and middle fingers were decently functional, the ring and pinkie fingers were not. That left me essentially trying to grip the gun with one finger, which works about as well as you'd imagine.
This might seem like a waste of time and effort now, but believe me, it's not. Thanks to cowboy action, I went through all this some time ago, but it's paying dividends now. Just last week, I lost an argument with a machine, and in the process lost the tips of my trigger and middle fingers on my strong hand. Fortunately, I already had a useful left hand.