Not really the epoxy glue would be a very thin layer.That is in effect what the epoxy is doing, no?
Folks are typically using stainless steel for the hardware.The washer itself is only there for strength and surface area not for conductivity and should have no influence on the conductivity. So what bolts do people normally use anyway, zinc, iron, stainless steel, tungsten,...?
We made a radar reflector product that used conductive epoxy to bond large pieces of aluminum. The machined aluminum parts were first “plated” with a chromate-conversion film that made them more conductive, then a 3-5 mil thickness of epoxy was applied between the parts to bond them. There are two formulations of conductive silver epoxy, rigid and flexible, and for this application we used the flexible formula mainly because it had a 3-hour working time. Both are available from McMaster-Carr at a ridiculous price.I just found this, inspired by @Sanwizard.
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I have not tried it, if it didn't work you would have a mess so suggest you try it with a couple of bits of scrap first.