Are there tools available for trimming PDF margins?

Problem

I have an ebook I'm trying to read in PDF format on a Kindle. Unfortunately, the page headers and footers have some content (page number and copyright info, respectively) preventing the device from scaling the actual text to match its usable area viewing area, thus leaving the actual content too small to read. Various tools are available which will trim off whitespace, but the Kindle already does this; my goal, by contrast, is to remove printed matter outside of a defined bounding box, and the only tool I've found for the purpose is moderately expensive commercial software. I could probably generate a mask in Inkscape; split out the individual pages using pdftk, apply the mask to each page individually (outputting to postscript), and recombine the numerous postscript files into a single PDF. However, this decode/reencode steps would be pretty unfortunate in terms of document size; something able to operate with a bit more finesse would be ideal. I have all major operating systems hand…