I’ve been working on various drills lately in order to achieve the straddle press to handstand and one of them is drill #5 explained in this video.
I start with the straddle position against the ground, which shares similarities with a regular straddle press, without being upside down. I put my back against a pillar to prevent leaning back in order to increase dynamic flexibility, which is the main goal of this drill. From there, just put your fingertips on the ground between thighs and lift your legs above the ground.
You may get some cramps in this position initially, but this move will help you increase that strength-dynamic flexibility which is the main thing you’ll need to perform the press handstand.
As you gradually increase your strength and flexibility, eventually you’ll be able to lift your legs with your hands between your feet and then soon you’ll be able to achieve that press handstand. You can do this drill for reps or time, whichever suits you the best. The results will be the same.