If this was an industrial control problem. I would try two things.
1: Mount a Tost CG release on the tow plane upside down and at an angle where the upwards angle of the tow rope would initiate a back release. The angle required, reliability, tendency for unintended operation,and whether or not this would actually work, to be determined by testing. Based on something like this that was attempted and reported on here earlier, I have a low confidence in this scheme working out.
2: Using a TOST release, add an electric solenoid activation device somewhere in the cable run to the release. The solenoid could be activated by a "full back stick" limit switch and a short time delay circuit on the tow plane, the normal manual pull handle in the cockpit, or a switch on the stick. Again, testing would have to be done to confirm that this scheme would actually work.
I have no idea how any of this could be accomplished given it's an airplane and the FAA is involved. Their requirements are baffling to someone that does not live in that world.

Ultimately, taking the human element out of the equation could prove impossible. The cure being worse that the disease is also a real possibility due to unintended consequences. However we have always done it this way, isn't a good answer either.