I've made a display "tacker" for my Nauteek 2000 Sail Computer. It mounts under the boom near the mast. It's a swivel bracket bolted to the boom with a short "tiller" arm extending forward. I have bungee line running from the tiller arm down to the mast rotator tiller. This triggers the swiveling of the display bracket. I also run a limiter line from the bracket to the boom...stops the swivel going too far on either tack.

Works extremely well.