Do you have Adobe Acrobat Pro? If so, you can use the "Detect and merge image fragments" mixup:
Bring up the Preflight tool (Tools>Print Production>Preflight), then switch to the "Single Fixups" tab and search for "merge". You should find the "Detect and merge image fragments" fixup. Now click on the "Fix" button and see if this takes care of this problem. You already know how to detect these "slices", so just check to see if you still have these slices after you run this fixup.
If this does not work (it depends on how close these image fragments are to each other), a custom plug-in would be able to detect the fragments in the documents that you are dealing with and combine them before you run OCR.
Karl Heinz Kremer
PDF Acrobatics Without a Net
PDF Software Development, Training and More...
http://www.khkonsulting.com