I run into the exact same problem with my print fulfillment website. I know Lee Jay and I have made the feature request several times each; Bill, please join us, the more the merrier.
Optional reading:
For those interested, a little background. Most of my event photos are purchased and processed through a third party's website. I generally offer 4 or 5 of the US standard enlargement sizes for purchase. We photographers all know that an 8*1' crop from a 4*6 original will chop the long-axis significantly, but only about 5% of my customers can figure that out on their own. While the website offers a custom crop feature, very few understand it or use it correctly. It would literally quadruple the effort, with very little return on investment, for me to upload custom crops for the various standard aspect ratios. So, I compromise with trying to shoot and upload standard 4*6s, that have the property of being 'safe' to default center-crop at the other standard ratios. After several tens of thousands, I can more or less do this 'by eye', but a custom cropping template showing these relationships, would be helpful.
