After two months of thrashing about I finally discovered that all of the necessary prerequisites to a ternary SR "Flip-Flap-Flop" have been solved problems for decades. No time to get into it now, but it turns out that voltage comparators have been used to implement primitive analog Flip-Flops for ages. With just resistor voltage dividers you can designate the flip-up voltage and the flop-down voltage to anything you want that your comparator can handle. I've now got working examples of flip-flops that range from + to - and from 0 to - with threshold levels very close to the ones I was already using. With any luck and a bit of ternary glue-logic I'll have a realized SR Flip-Flap-Flop in short order.