I saw one other post about this in the Bar Sport forum, but it was old and I didn't want to necro it, so here goes.
What about using a 3D printer to print the plastic onto copperclad, then using etchant solution to remove the copper? Would the PLA/ABS come off in the solution?
Any other material that can be melted and applied in a similar manner?
How about using wire solder in a nozzle heated enough to melt it? You could brush the board with a thin layer of flux prior to printing it with lead to make it stick better.
73, David Boucher, KD0PLS www.arrlmidwestconvention.com