substiture exercises for improving presses? PLS HELP

Which muscles are mostly needed in stalder presses?

If you have someone who knows the movement, is flexible enough, and is able to hold a handstand. which exercise would help him in getting his stalder press to handstand or make him stronger at the movement so he can do more reps? s

So what are I am basically asking is if there are exercises (which are not presses themselves) which can really help in improving one's ability to press, so he/she can do more repetitions?

Thanks a lot!

Handstand 2 course was created specifically to address stalder press deficits and to fix them.