How to buffer charge d~u while doing back+k?

I trying to do this while playing Ash in KOFXIII

Use a diagonal like :db:, so :db: B then :u: to get the :d: :u: flash kick motion.

Or go from back to down while back + B is coming out, then go to up once you’re holding down. “Like Guile tricks in SF4”, at least that’s what this vid and the comments in it seem to say.