Continuing to use damaged cones in rear hub?
No it would not work. The pitt didn't form just because it was on the bottom, the pitt formed either because the cone came loose, or an abrasive got into the bearings.

There's an equal amount of force being applied to the top of the cone as there is to the bottom when your hubs are properly adjusted. Think of the components in a hub as a stack, the cup is both the top and bottom of the stack, and the balls and cone are sandwiched in the middle, put some weight on the top of the stack and the force is going to be evenly distributed through everything. Your theory would only work if you left some play in the hub, which would only destroy the cones faster. 

Replace the cones and balls, they're cheap, and I imagine that you don't want to have a reputation of being a hack mechanic.