I find this move the easiest to RC…i do by using the thumb and index finger to start the roll, while keeping the right side of my hand up abit , then push my hand down while keeping my fingers up, pushing the mk and rh with the part of the hand underneath the knuckles.
i do it the ghetto way and i get it 99% of the time.
all i do is basically, take my entire hand and mash all the buttons, starting with the roll buttons, then land on the rest one after the other (mk, hk).
so it goes like this: lp+lk, mk, hk
but remember, you have to use your entire hand, and just roll your hand over the required buttons one after the other.
it looks stupid and ghetto, but damn its the easiest way to do it.
I found that the method that Kcxj showed was the easiest for me. Placed your index and thumb closed together on the jab and short and place your knuckles on top of medium and RH and perform the roll method. After you have tap the jab+Short roll your fingers across Medium and RH. hope that helps:p Also try going into practice mode to have Ryu throw FB at you and keep practicing you get it after a few trys