Some folks have had success by removing the oil gallery plug on the right-hand side of the engine above the points cover and filling it with oil.
The sure-fire method that worked for me was to drop the oil pan and remove the pressure regulator from the oil pump. Put a quart fo oil in the tank and kick the bike until oil starts to come out of the relief passage in the pump. Reinstall the regulator on the pump and pour some oil into the oil pan before reinstallation. Refill the oil tank the rest of the way and kick the bike over a few more times to get the oil moving through the galleries.
