Woops, I should have said you could use either X or Y, w.e you prefer, I do everything with X except multishining with fox.
I can do shdl like m2k, I think he does it with X as well, im not sure, sometimes it looks like he flicks the control stick up.
Here take a look
Also, I would not look for an specific way for moving your thumb like this and that, instead focus on what best works for YOU and only YOU, and then just be patient and practice. I suggest you learn the motion without playing the game to build finger speed, once you have repeated the motion many times, your body will adapt and your thumb will get faster.
Something I like to do is repeat a certain motion for about 50 to 100 times and try to go faster and faster, for instance the first 20 or so I would do it slowly then I'll increase the speed for the next 20, when I'm about to finish the 100 repetitions I'll do it as fast as I can even if I loose a bit of control here and there. This tells your body (after some time) that it needs to get FASTER. After doing this I'll play the game and see if I had gotten any better, most of the times I can notice some progress but after a week or so the difference is huge.
Been doing this recently to perfect some techniques like moonwalking, and I've been very successfully, took me a couple of days. But you have to be consistent.