Cheapest solution: Leave the bathroom door open. Close door when using. I think the only way you could run a line in there would be to tee off a nearby run.
2006 23B Hybrid with 10k round bar WDH
2011 F150 4x4 SCREW Ecoboost, Max Tow, Integrated TBC, 3.73 LS axle, Firestone Ride Rite airbags.