I have an idea for a switch puzzle, I don't know if you've tried this before or not: can there be a fixed part? I've made a simple one I call Simple Key, here's the shape and sequence:

This is the bound shape notation with the FMN loop. The sequence will form bonds where it's supposed to (and the FMN loop), but will misfold into a stronger shape instead with a multiloop where the bonding site is. Here's the misfold shape (unbound target):

Obviously you can refine the shape as you see fit, the idea is to have a part that's not shifting, and the bonding site is an ideal splitting spot.

.......(((((.....(((((......((((....)))).....))))).....)))))........................

GGAAAUACCUCUAAAAUUCGGAAGGAUAUUAUGAAAAUAAGAAGGUCUGAACCUAAGAGGAGGUAAAGAAACAACAACAACAAC

This is the bound shape notation with the FMN loop. The sequence will form bonds where it's supposed to (and the FMN loop), but will misfold into a stronger shape instead with a multiloop where the bonding site is. Here's the misfold shape (unbound target):

.....(((((((...((((....)))).((((....))))..((((....))))....)))))))...................

Obviously you can refine the shape as you see fit, the idea is to have a part that's not shifting, and the bonding site is an ideal splitting spot.