Yea, agreed it's pretty hard, though with some tradeoffs it could be done pragmatically.

I would probably slightly overbuild the plastic and then use a heated tool to form the smoother surfaces the wire/foil would go in/on.

I've also seen laser sputtering of copper, etc. which could be the another approach, something similar is used for metalizing plastic already, though contamination would need to be controlled to maintain low resistivity.