Long ways between command at the front, and action at the rear ..

Update? what have you tried already?

you ask:
Any? well I love the self-contained nature of a Rohloff hub, all the index sequencing is in the hub.

so a long cable run is not altering the shifting lag significantly.

not much help , I know, buut a thought to share nonetheless..

Your, having gone down the derailleur path, how about an electronic Di2 shifter conversion ?,
to eliminate the mechaanical lag of the cable entirely.