AFIK, the "official" Printrboard is a multi-layer board, so I'm guessing that the dead-end trace actually just moves to another layer. After all, the boards do work!
So I agree 100% with you: you'll never be able to repair a trace that's internal to the board, so you might as well just run a jumper wire.
Your problem reminds me of a situation I ran into about 35 years ago. At work, I had designed a PCB and etched it using fairly crude "homebrew" equipment. It looked good, but before populating it, I wanted to check it out with an ohmmeter. All the places that were supposed to be connected were connected, but there was one undesired connection between two unrelated nodes. I searched and searched for the wayward hairline connection with a microscope but couldn't find it. I took a tool and scraped along the gap between the traces and still couldn't fix it. Finally, I figured that whatever was causing the undesired short circuit must be very tiny. So I connected the two traces to opposite sides of 110VAC. I never saw a flash or a puff of smoke, but the undesired short circuit magically disappeared! The board worked fine.
Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick