Here's a little hack that will enable you to add products to Ubercart by passing an array of product ID's and quantity of each product specified. Relies solely on the uc_cart_add_item(); function. Works great in content nodes that you've enabled PHP input on.
<?php
if(!empty($_POST['products'])){
$products = $_POST['products'];
foreach($products as $product){
if($product['qty'] != 0){
$pid = $product['pid'];
$qty = $product['qty'];
//uc_cart_add_item(2, 3);
}
}
}
?>