Detection of Peanut Oil During Autopsy?

I'm writing a mystery story. An elderly man apparently chokes to death, but the death is shady (lots of people had reason to kill him) and an autopsy is performed. Some bones are found in his throat, indicating that it was an accidental choking, and the police are satisfied.

But the way I want the story to go, someone actually coated the bones with peanut oil, and the man has a serious peanut allergy which caused his throat to close up and made it certain he would choke. The killer nearly gets away because the coroner misses the peanut oil.

My question is, would the autopsy detect the presence of peanut oil in the throat, if the coroner wasn't specifically looking for it? If so, might there be some way the killer could administer the peanut oil without it being detected in an autopsy?

Thanks in advance, I didn't know where else I could ask such a question until I found this site. And no, I'm not planning to kill off any of my elderly relatives with peanut oil. :)