Remove hidden information without converting to RGB

I'm preparing a PDF for one-color printing, and it has some color data off the page that's messing up our prepress process. So I ran "remove hidden information" to cut that data out, but it converted the entire file from CMYK to RGB. I obviously need the file to stay CMYK (getting it down to just K was the whole point). Is there any way to remove cropped/overlapping data without converting to RGB?