Anyone knows how to print mylar membranes like those in model M?

[DMA]

Yes, your guess is correct - I want to replace a membrane in my Unicomp 103 with something like FEXT PCB - only not PCB, but membrane.
Looks like TrioMate connectors will work with conductive layer on both sides of FFC, so it may even be a SINGLE SHEET of mylar, printed on both sides (If technology supports that - it may be limited to single-side printing, in which case there must be two sheets, bonded together somehow).
In any case - I suspect it's way cheaper than PCB and actually more suitable for triomate connectors.

The idea is so cheap and stupid it might just work. Not posting this to model MF thread because enough scope creep there as it is. But it may work for phase 2 and I can test my stupid ideas on myself, can't I?