This cannot be done with Resize but it can be done with Imposition and Preflight.
Caveat: This will work for documents in which the height is less than 5x the width. The workflow would have to be modified sligthly to support documents in which the height is more than 5x the width.
Impose the document 1up to a custom press sheet size of 40 x 200 and then change the Page Scale Mode to Fit the document to the defined press sheet size
FreeFlow Core defines new PDF boxes on imposed documents. This allows the system to retain an understanding of where the original document is placed relative to the larger press sheet size:
The preflight component then executes a preflight profile that resizes the cropbox to the dimensions of the trimbox
The result is a PDF that's been resized to 40" x Automatic (in this case 40" x 53.33").
The resized PDF and the workflow have been included as attachments.
Received the following question in the internal FFCore forum
I have a customer that has just purchased a 40" wide format printer. They want to upload documents of varying sizes to FFCore and have Core resize the width of the document to 40" and have the height resize proportionally the same amount to whatever height. I tried to set up the Resize Pages to do this but couldn't get it to work - my Resize Pages always create a PDF that is the Width and Height specified in the Resize preset. Is this possible with Resize Pages?