Cropping Pages and Extraneous Data

As part of my job, I often crop two-page PDF spreads into single pages to assemble into new PDFs. My employer recently discovered that even after using Acrobat to crop the pages, the file still retains all the data from the spread. This makes the file much larger than it needs to be and means that data-driven PDF readers can still view the entire spreads.

I'm using Adobe 8.1.5 Professional, and have been using the PDF Optimizer to try and remove this. "Discard all alternate images", "Detect and merge image fragments", and "Discard hidden layer content and flatten visible layers" seem like they would be the solutions, but don't fix anything.

Does anyone out there know how I can shrink an PDF file's media box to match the new crop box in Acrobat?