Recently, however, I've started playing with a little variation. I'll use my right hand (the collar grip to do the light "on/off" action to uke's shoulder as he's stepping back. Then, instead of using both hands flicking back to get him pitched forward, I'll simply lift my left elbow. The right hand stays out of it, and my left does literally nothing more than raise the elbow (the hand does nothing).
Using both hands, it seems, you get a fairly even reaction, and as Nick says, you can jump in there for any number of throws. With the method I just described, uke's reaction tends to be somewhat lopsided. I "tick" him to his back left corner, then "tock" him to his right front corner. Mostly, it's a nice set-up for harai tsurikomi ashi, just a little more diagonal. The elbow or the wrist do basically the same thing, I think, but going one side then the other creates some interesting vectors no matter which way you step (stepping around for a double foot sweep, etc.)
And along with it, I've been playing with changing up my stepping pattern. At the same moment I lift the elbow, I also take a slightly truncated, shorter step than what I had been doing, which exaggerates the forward pitch. This sudden change in the length of my stride has always been a fascination to me lately, but shorter AND longer.
Anyway, if you have a chance to explore the rest of these videos, DO. They will revolutionize your judo. Beautiful.