If you want to get better at lifting weights, lift weights. If you want to get better at stunting, then stunt. However, there are some exercises that have increased my toss. Grab bench press bar (or curling bar) and place minimal weight on it, may 25 lbs plates on each side (perhaps 15 for female). Stand with back straight and feet shoulder width apart, bend your knees slightly allowing the bar to go just above your knees the stand and pull the weight to the top almost like a clean and jerk. Make sure the elbows lead the wrists upwards until the very end.
Want to get better at holding your flyers lines while in a extended stunt? Try to BALL/BALL/WALL Drill. Get a small medicine ball that you can hold firmly with one hand and a large inflated exercise ball. Have a friend hold the exercise ball against the wall while you position yourself on the other side of the exercise ball positioning the medicine ball against the larger ball. While maintaining a lock out arm lean into the line of balls against the wall slightly to apply pressure. Then have your friend release the larger ball and you will feel a balancing act occur. Maintain this line and control is a simulated weight distribution and maintaining of line balance that you will similarly feel in a cupie. **WARNING- only lean in a little at first , applying all of your weight in the beginning could result in you taking a nasty fall into the wall. Best of luck.