You could try Fiebing's alcohol-based leather dye. You probably want to hit the surface with 4/0 steel wool to give the dye something to adhere to then apply the stain with a rag. You'll probably have to go very dark as most of the stain will wipe off. Another option might be to try mixing one of the powdered stains with the oil you used to finish the stock. Again, you may have to go darker than your desired end result.

Good luck and have fun experimenting...

Phil