Per-canvas comments

The document data section allows for adding non-printing comments that apply to an entire document. Is there a way to add per-canvas comments? I’ve been experimenting with a notes layer, but it impacts the canvas size when exporting a PDF.

I’m exporting PDFs from OmniGraffle for use in MS Office documents, and auto-sizing of canvases has otherwise worked great.

A note layer (or hidden note shape(s)) probably gives the best solution.

Beyond the name string, canvases don’t, I think, have any other user-writable text properties.

Perhaps post production PDF compression ?