That wouldn't be too hard .... you'd need to clone the shipping estimator and modify it so it used a GET passed product reference instead of looking in the shopping cart ... then just use a variant of the code on the shopping cart page.
Something like this would do it:
Code:
<div class="buttonRow back"><?php echo '<a href="javascript:popupWindow(\'' . zen_href_link(FILENAME_POPUP_SHIPPING_ESTIMATOR_PER_PRODUCT,$_GET['products_id']) . '\')">' . zen_image_button(BUTTON_IMAGE_SHIPPING_ESTIMATOR, BUTTON_SHIPPING_ESTIMATOR_ALT) . '</a>'; ?></div>
BrandTim