There are two ways i do it. BOTH with straight arms.
1. there is the horizontal one (quite hard) the way to do this is to just have good arm and shoulder strength.
2. The verticle one (easy) you still have straight arms but you have your waist bent so your legs are facing verticle. you still use the same handling though. the only part that is a bit hard about this one is getting up there. once you are up it is soo easy.
As said before it requires a lot of arm, shoulder, and core strength. Look at any pick of it being done it is not that hard, at least in my eyes, to comprehend. Like a sideways hand stand. Bottom hand is support top is gripping.