There is a silver conductive ink option that may work but I have not tired it yet.
https://www.youtube.com/watch?v=EBlqPS8boLIIt takes silver acetate, formic acid and ammonia though the silver acetate can be made from silver nitrate and sodium acetate, all fairly available on the net. I think one wold have to just place a drop on on each hole let it dry then heat the board to sinter the silver. Dipping the entire board would most likely result in the silver being reduced by the copper and plating on the entire surface but I am not sure. Then there is always the graphite ink (black hold) method, it works but messy, not tried that one either.
Craig