I'd still do it with the extra get parameter.
Let's say the url for the first landing page is
and the url for the second landing page is
save it as includes/templates/your_template/templates/tpl_product_info_display_b.php
modify it to display your product differently from the standard.
Now, edit includes/modules/pages/product_info/main_template_vars.php
Find this line of code:
modify it to be
$tpl_page_body = '/tpl_product_info_display.php';
that way the new template file will be used if and only if the &lp=b parameter is in the url. Same product from the database, just displayed differently.
$tpl_page_body = (isset($_GET['lp']) && ($_GET['lp'] == 'b') ? '/tpl_product_info_display_b.php' : '/tpl_product_info_display.php');