Not used DE but i have used

A stiff Powdered chalk paste smothered into the inletting and allowed to dry out will slowly draw oil out of the stock, if you do it a couple of times you can get really good results. To remove it just warm water and scrub gently with a tooth brush.

Or Acetone as suggested.

i can't see why wood ash wouldn't work. When removing oil from the head of a stock i sit it by the range or wood burner ( not too near ) and have it in a cradle with the head facing down to try and encourage the oil to run out.