I have used Acetone, MEK and Napther to soak the oil out of woods. I no longer use the MEK due to the possible health hazards, but the others work well. I have soaked grips/stocks overnight, and in some cases could see no evidence of oil the next day. Some are oiled up so bad that all you can expect is for the process to lighten it up a bit.
I recently refinished a Lemon wood stock. It is light blond, almost yellow. It had been standing in a closet for years. The lady I bought it from said her husband had not cleaned or shot the gun for over twenty years, She said he would take it out and rub some "motor oil" on it occasionally. As a result, the pistol grip was a dark brown, with streaks almost to the butt plate. I first stripped the wood with a furniture refinish product, I then soaked it for 24 hours in napther. I took it out and let it air dry in the shop, went over it with 0000 steel wool and applied the finish. It looks almost as good as new. There is still a trace of oil stain, but if you didn't know it was there you would never notice.
A word of caution...........IF YOU USE ANY OF THESE PRODUCTS---MAKE SURE THE WORK AREA IS WELL VENTILATED. I DON'T RECOMMEND USING THEM IN THE HOUSE, UNLESS YOU KNOW A GOOD DIVORCE LAWYER.