I just stuck it over the lower half and sealed the whole lot with putty.
@RafalFett pointed out here that the visor material on the original helmets actually has a cut-out for the circuit board, and covers the sides along the board. So in my infinite insanity, I'm trying to replicate that. I've also figured out a recipe for a putty that looks like what they used on ESB and will put that on after I get the visor correct.I just stuck it over the lower half and sealed the whole lot with putty.