Just so we are clear. A porous barrier is not a salt bridge. A proper salt bridge contains its own special electrolyte(the 'salt') distinct from that of the two electrodes.
The point of a porous barrier is just to prevent the two electrolyte solutions from being mixed by any bulk motion of the fluids, ie stirring, convection, etc, while still allowing diffusion. Holes that were multiple mm in diameter would be rather bad at preventing bulk flow. You should be able to print somewhat smaller holes with polyholes, but I'm not sure if you could make them small and numerous enough for good performance.