How feasable would it be to add an option to pdfload to specify which of the PDF boxes to use when reading the PDF?

Our usecase is creating thumbnails from PDFs with printer marks on, we want to use the trim box so the thumbnail is what will be produced off the back of a guillotine (rather than the current default which shows what will be printed including the printers marks).

This comment (#379 (comment)) explains the PDF boxes well.