For 4x5 pano it may be more financially prudent to shoot the full sheet and mask/crop when printing/post processing. You can change aspect ratios from 5x4 to 5x2 (eq 5x12 or 7x17 enlarged) or 5x2.5 or 5x3.5 (1/2 5x7) . You can buy dark red polyester sheets at your art supply store and cut a permanent window mask for your enlarger's film carrier. Then there is also cropping by using the blades of your easel or crop tool in software. If you need a visualization aide for the field, print/draw lines on clear sheet sized to fit on top of your ground glass while you compose.

Your pano tastes/vision may one day change or a need arrises for more of the image to suit another use. For advertising they sometimes bleed the excess portion of the image through a slightly transparent banner.