I actually learned these the day after I learned handdrag 3s. You really just need to set the spin harder and be prepared to feel more "off axis". I recommend trying them off a hip jump if you have one that you can access, or even a small jump, as opposed to a knoll or roller.
to me their pretty easy, i first learned handdrag threes then ended up reverting 180 whenever i landed so i just through that into the rotation. just go relatively fast, kind of crouch down hop onto your hands continuing the rotation and yeah, just remember to spot your landing and you're set
......... and remember to afterbang.... even if you fall!
snowboarders are more rebellious then you will ever strive to be- spork.