I hope this isn't a silly question, but am I correct in assuming that there is no possible way to reposition the control arms and or the spheres when a joint moves by using an ERC morph?  I've tried and came up empty.

I seem to remember a discussion about this some time ago, possibly in the old Poser Pros forum; wherever it may have been, the conclusion was that it wasn't feasible. I'll watch this thread and keep my fingers crossed in case there have been any recent developments, though. :)

It would be nice if it could work.  In certain poses, it often looks like a bending morph is needed, but many times, just a simple adjustment of the control arms will improve a joint bend.  If this could be done automatically, I would think it would be more economical than adding morph deltas.  In any case, thanks for the reply EB, much appreciated.

There is an actor callback for vertices that might give you a way in .

There is no way to do it with ERC. Looks like markschum is hinting that it might be possible with a py script. The only thing I can think of that you can do with joints and ERC, is to make a sort of psudo joint center that you can move around. The problem with most things in the joint parameters is that they are not driven by dials (or more correctly speaking a 'keys' value), so there is nothing that ERC can act on.