One thing that helped me learn to release was to retrain my elbows to move independently of the rest of my upper body. It sounds silly, but most people lock their elbows and forget to use them as their own hinge. Pretty much all you do is canter around in half seat over the occasional ground pole. When you get a to ground pole, unlock your elbows and move just your hands forward to provide a release. Nothing else in your upper body changes. Just move your hands forward over the pole. Do it until it is automatic and ingrained in your muscle memory. If you want to add a second element, grab mane each time your provide your release since you will probably want to do that over real fences anyway.
Another thing you can do is picture riding on a merry-go-round with you holding the pole of the horse you're on. Shorten your reins and move your hands forward to that position and canter around in half seat like that. That will get you started toward the proper rein length for jumping. Most riders ride around with their reins too long between fences and then have to make a huge move over the fence to follow their horse. If your hands are already forward, all you have to do when jumping is soften your elbows and press your knuckles alongside your horse's neck over the fence. It's much more subtle and effective.
As for your jelly abs, pilates a few times a week will fix that.
You just have to see your distance...you don't have to like it.