Uchimata sukashi, translated as something like, "slipping the inner thigh throw," is another non-technique. It is really cool when it happens, but it is not really a skill or a principle, so does not really deserve a lot of practice or a place in the Shinmeisho no waza. You just try to figure out when the other guy is going to do uchimata and then step aside so uke can bust himself for you.
I remember one of the guys I used to practice with a lot had a bad hang-up about sukashi. This was part of his rank requirement for his next rank but he'd been hurt by a clumsy sukashi so he decided that all sukashi was dangerous and shouldn't be practiced. He was willing to forsake ever ranking again to avoid this one thing. I told him, "Look, knucklehead," (or something like that), "you just step aside then do sumiotoshi just like you practice all the time in aikido. There's no magic in sukashi."
"Oh..." he replied and went back to practicing the thing, conveniently renaming it sumiotoshi in his mind.
So, sukashi is another thing that I don't teach. If someone asks about it, I tell them to step aside and do sumiotoshi, which they already know.