You could make a bunch of virtual copies and then crop a different person in each copy. Then you could export all the virtual copies and create finished images.
Alternatively, you could create Snapshots with the different crops in Develop. But Jim's suggestion is probably how I'd do it.
Another method to try: set this up in a Custom Picture Package, in the Print module.
That can show parts of images visually on the fly, without actually cropping them (or virtual copies thereof) for real, if you see what I mean... which cuts down on the number of virtual copies needed.
Then the Print job can be set to output to JPG, of the desired resolution and attributes, as an alternative to sending it to a printer.
OR - just a thought - set up a dummy Book and then output that to PDF.
Either way, you can zoom and slide pictures around, each one within an image cell of a chosen shape and size on the page - which effectively acts as a "window-frame" onto that image. Without having previously cropped that image down in Develop.
IIRC you can save the completed layout (in the case of Print, as a Print Collection) so that you can come back to it - though I cannot test this out just now. And IIRC with Print / Custom Package you need to press a modifier key (maybe Ctrl?) in order to pan an image around inside its windowing image frame, instead of sliding the frame itself around on the page.
You'd need to set the dimensions of the jpeg in Print Job to suit the crop you needed Richard, but yes, you could do that as well.
Thanks everyone. I'll give the different methods a try.