Someone outside of these forums was gracious enough to point me in the right direction, so here's the answer:
Open up recommends.php, then find the line that starts:
Code:
$products_id = func_query("SELECT $sql_tbl[products].productid FROM....
Then, further on that same line, I added the following (in bold text):
...AND $sql_tbl[categories].categoryid = $sql_tbl[products_categories].categoryid AND $sql_tbl[categories].avail = 'Y'
AND $sql_tbl[categories].categoryid != xxx AND $sql_tbl[categories].membership IN...
^xxx being the category id you want to exclude from the recommended products results.
Cheers