Wow that's a challenge - so many angles and dimensions to change in the mainsheet assembly based on the angle of the boom.

If it's a showstopper, though, how about a quick dirty solution until you solve it: provide different static props (including the mainsheet assembly) for say four points of sailing on each tack.. i.e. close hauled, reach, broad reach, run... or whatever.

I guess you probably already thought about that though.

PS: a spinny would be great too!

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)