I think you've got to try to soak up the oil itself. I'd say to try either VERY FINE sand, or the old fashioned, non-clumping, clay kitty litter on the floor--they use these in some service stations to soak up oil spills, so it should work for you too. You'll be able to see it actually darken. Scrape it or sweep it up and put down another layer--keep doing this until it won't turn dark anymore--PLEASE DON'T RUN A VACUUM OVER IT UNTIL IT DOESN'T DISCOLOR ANYMORE. A SPARK WILL MAKE YOU WISH YOU HAD THE SMELL BACK.
Do you mean that some got ON the walls, or literally IN the walls--back behind the plaster or dry-wall? If it's on the floor back there, I'd use the sand or kitty litter there too--if it's on the walls themselves, I don't know what to tell you--maybe a white vinegar and water solution could neutralize the odor.
Beyond these things, I'd say to open every window and run lots of fans--put some so that they blow directly on the areas where the oil spilled and others up in the windows blowing out, so they pull the air inside to the outside. I'd start with the fans blowing out right away, the ones blowing on the spots can go after you've soaked some of it up. Good Luck with this!