Alternatively, you could build a preflight profile to crop the PDF to visible content.
There's a fixup in pdfToolbox which you can use in the Preflight component to enable this
Once the document has been trimmed, you can impose 1up per above and center the content on the page that way.
Depending on what the PDF looks like there may be multiple ways to do this.
For example, if the PDF came from a program that added proper trim marks (in the "Registration" color space) you would use the option in Optimize to Define the page geometry boxes based on Cut Marks
After that you could impose 1up to an Automatic Press sheet size (do not select any size options) using the trimbox for imposition and adding a 1" margin all around. That will reset all the other boxes and center the content on the PDF using the cut marks as a guide.
