I too have been experimenting with using nylon fishing line for wiring
foundation as I sometimes use formic as an alternative to strips for varroa
control and it should be unaffected by the acid.  I put the unwired
foundation in the frames and wire the frames so that the upper strand lies
close to the foundation on one side and the lower strand the other.  The bees
draw the foundation around it.  Early days yet but so far, so good.
Chris Slade