I've been playing with this whole Fudo/Sochin dachi blading vs. non-blading phenomenon, and believe I came up with a pretty simple way to work on it. Actually it was inspired by Sochin kata, which executes the kind of hip movement from these "rooted stances."

In Uechi kata, lateral elbow strikes are always off the front leg. In Sochin kata, they are always done off the rear leg. There is no way to do the Sochin kata rear elbow without bringing the hips completely frontal. Meanwhile, blading just a bit makes a front lateral elbow a bit easier.
So...
What I have been drilling my students on now is a play on the Kanshiwa kata wauke and elbow, only I have them alternate sides. From the right rooted stance, they do left circle and right elbow. Then they do right circle and left elbow. (Later I have them switch stances.) I tell them to try keeping the circle on the plane forward (waxing the mirror in front of them), but let a slight canter of the hips one way or the other drive the elbow. By doing this simple sequence and nothing more, the student can concentrate on keeping the knees out (in the rooted stance) while cantering the hips back and forth. The torso alternately blades (front elbow) or goes frontal (rear elbow) with the techniques. And it takes very little movement to get a desirable effect. I actually had to stop after 4 or 5 reps on each side as my forearms were getting bright red from the contact of forearm on the other palm.
I am tempted to pick up Sochin kata from the video I posted in this thread. (Thanks, Van!!) Nice kata! It works a lot on one of the very hip movements that I'm talking about. And it keeps it pretty simple. There are more degrees of freedom in Sanseiryu, but the Sochin kata approach at least gets you started.
- Bill