I was watching the 3 Dimensions of Shaolin last week, and he shows a no-gi reverse omoplata on the second disc. He uses a setup similar to the I do (pinning the arm while passing guard and flipping them over all fours), but he doesn't step over the arm to trap it first--he just pins it with his knee and gets the crucifix (which is the start of the reverse omoplata) after the flip.
I do this sometimes, and it was the original way I did this move, but I found I was having too much trouble getting their arm into the right place for the crucifix. If you pin with the knee and have trouble getting the crucifix you can always switch to taking the back (like Marcelo shows in his second set) or just start playing a harness game.
It can also be hard to step over the arm to trap it (like in my setup) so both ways have pros and cons, and you should just go with what you can get.