I wasn't able to get any practical ideas on the forum, so I came up with a possible solution. We worked through a couple of issues out at Synergy and ultimately developed a usable jettison mechanism.
We had wanted to use a threaded-end push-pull cable like this one
from ACS, but due to the requirement for a good bit of movement at the actuator arm, we ended up with a Bowden cable. It works well for the pull (jettison), not so much on the push (to reinsert the pins). For that we have to reach under and help rotate the actuator arm as we are pushing the cable in. Given that the primary goal of the solution was an emergency jettison mechanism, we accepted the compromise for the very occasional requirement to remove and reinstall the canopy on the ground.
We located the handle on the sub panel above the pilot's left knee and has a locking button - so the likelihood of inadvertent actuation is fairly low.
Sorry about the blurry pictures.