Ok this is what I've been busy with lately. After much thinking and discussion with some Erhu instructors, I've created a video on how to do the rolling vibrato. The video is divided into 3 steps: (1) finger movement (2) bowing (3) combining finger movement and bowing.
Each step should be mastered before moving on to the next. And master each finger first before moving on to the next. It is a slow and tedious learning process but it beats having a convulsion every time you do vibrato.
And there is no substitute for a face to face lesson with a Erhu teacher. You should get a teacher to tweak your moves whenever you have the chance.
Here it is:
4) How to do rolling vibrato on Erhu
The rest of the earlier videos are here:
1) How to hold a Erhu Bow
2) How to bow the Erhu
3) How to play the Erhu - Left Hand Position