If you are gonna go to all that trouble, why not put a trim tab on the aux rudder and drive that either with a small a/p, or better, with a horizontal axis wind vane?
When I was outfitting Insatiable I for cruising many years ago the budget
was limited, and I built my own aux rudder vane system. It cribbed the push-pull cable drive for the trim tab from the Autohelm
vane (now marketed by Scanmar). The rudder was built much as you are proposing, the trim tab hung in little teflon bushings, and the whole thing cost less than 300$ for materials (this in 1985). The vane drove the boat whenever at sea, and sometimes when coastal/daysailing, and had over 50K miles to its credit when we sold the boat. I really miss it!
So, have a look at Scanmar's website and consider the possibilities.
I'd be happy to answer any specific queries.
Jim and Ann s/v Insatiable II lying Michaelmas Cay, Qld Oz