I did the assembly for tj_gee so I might as well chime in here and bypass the middleman.
Find longer metal screws and use metal washers between the screw head and the plate to secure the plate to the case without really touching the pcb
You mean plastic/paper washers? Wouldn't a metal washer just short the circuit again?
What I meant with my last of 4 possible solutions (quoted above) was something like this, expertly drawn, cross section:
http://i.imgur.com/X1ufizC.jpgThere would not be any metal touching the top of the PCB which seems to be where the short is occurring. I'm not positive there's enough space between the switches on top of the plate to squeeze a washer anyway, so this is all mostly moot, but of the 4 options it keeps the metal the farthest away from the exposed connection.
I'll have to see if the standoffs suffer the same issue as described by kawasaki161 but I don't think they do; I'll validate tonight.
FWIW I have conferred with my EE cousin and he said nail polish, super glue or a conformal coating (most often used for waterproofing PCBs) can be used to cover the exposed trace and then a non-conductive washer will suffice. I'll probably go with the superglue as I have several varieties on hand already, and then either foam or paper washers on top of that (and maybe under the PCB as well, if necessary)
Thanks all for the feedback and suggestions.