Just to update this, a while back, what I did was added a checkbox that deletes the field data when selected.
I simply changed this on the Update function:
if (isset($_POST['delImg'])) {
$UpdateQuery->bindColumn("prod_img", "s", "".($WA_DFP_UploadStatus["WA_UploadResult1"]["WA_UploadResult1_1"]["Name"]) ."", "WA_BLANK");
} else {
$UpdateQuery->bindColumn("prod_img", "s", "".($WA_DFP_UploadStatus["WA_UploadResult1"]["WA_UploadResult1_1"]["serverFileName"]) ."", "WA_BLANK");
}
Not sure if it's good practice but it works fine for this purpose.