I don't think you'll get the grease out of the leather once it has soaked in. You could soak the whole thing in oil to even out the color. Sheldon Brown describes how to soak a brooks in oil on this page:
http://sheldonbrown.com/leather.html
You can remove the dye from a leather saddle with laquer thinner. I "pre-aged" a green saddle that way and sold it at a bike swap for more than I paid for it new.
