Well.... ready to have some fun?
When you say "root categories" I take it you are talking about your primary or "home" page, yes?
Your home page is basically, welcome.tpl ---
what if you were to make a new file, call it, "homepage.tpl" and call it from welcome.tpl ?
{include file="customer/main/homepage.tpl"}
IF -- and only if, you are using a SEO mod, such as CDSEO, where your product or category pages are called by a unique URL, then you can get away with this... and simply link to your product directly from the homepage.tpl
Am I understanding what you're trying to do?