In case anybody's interested, here's the workaround I did (only works if
vb and pp are using the same database). In inc_features.php, I changed all the mysql_ calls to vbulletin's built-in database class, so all the mysql_query calls become $db->query_read, mysql_fetch_row becomes $db->fetch_row and mysql_free_result becomes $db->free_result. This way it uses whatever method vbulletin is set to use (in my case, mysqli).