I don't use Lightroom, just Adobe Camera Raw, but shouldn't Lightroom see the crop made in PM when you import the photos into it from PM? At least if you use the correct settings for metadata, Adobe products should (and Camera Raw definitely does) see the crop made in PM automatically. That's one of the strengths of PM, I find I can do the cropping inside it very quickly, and when toning the photographs in Adobe Camera Raw, I already see the cropped photo.