individual canvas size for layers?

[s1wurm]

I'm working on a huge (14'x8') image that I'm slicing down into individual standard US Letter size fragments. I need to export the layers created this way to a PDF with each layer as a page. When I do this, the individual pages it creates seem to keep the main canvas size of the huge image as the page size, rather than the boundary of each layer. Is there anything I can do to make each layer's boundary the size of its page in the PDF? I'd like to avoid having to manually crop each page, since there are 224 of them.

Thank you in advance!