You can try placing the Product Detail module on a separate page. This will be like your secondary module so make sure the other original one is marked as Default in the module's settings. This new page should be a simple page with minimal skin. Then if you follow the similar URL as the other product detail, you can point to different product just by changing the URL. Please note when you add to cart, it will normally want to point a link to your cart page so you might want to customize the Product Detail display template so that it behaves differently like open a new window, etc. Give it a try!