You know what else conducts electricity really well? Gold.
Maybe put out (part of) the hoard for the PCs to encounter before they get to the dragon. If some of them start rifling through the pile looking for magic items - or going the full Scrooge McDuck - then the dragon can just take a pot-shot at one far corner of the loot pile, from out of their line of sight, and it'll arc through the whole pile and fry anyone who's touching it.
Optionally, they may also get splattered with flash-melted gold.