[McGuireArmyNavy]

I know it's been a while, but since this is the thread that showed up while I was searching for this, I will post my solution here.
I'm sure that someone more experienced has a more elegant solution, but here is what I did in 4.6.4
[edited to add] On /product.php, around line 89 [end edit]
after

PHP Code:

if ($cat > 0) {
    $is_product_cat = func_query_first_cell("SELECT productid FROM $sql_tbl[products_categories] WHERE productid='$productid' AND categoryid='$cat'");
} 


I added:

PHP Code:

$sec_cat = func_query("SELECT categoryid FROM $sql_tbl[products_categories] WHERE productid='$productid' AND main='N'");
$smarty->assign('sec_cat', $sec_cat); 


Then, on the product page (/common_files/customer/main/product.tpl around line 50) i put this

{foreach from=$sec_cat item=sub}
      {if $sub.categoryid eq "???"}<p>LOREM IPSUM</p>{/if}
{/foreach}

obviously replace ??? with the categoryid you're looking for, and the LOREM IPSUM paragraph with whatever you want to show on the page.