libs/ubbthreads.inc.php

function generate_rss_feeds

find:
PHP Code

$posts['POST_DEFAULT_BODY'] = $html->truncate($posts['POST_BODY'],$feed_include_body);

add below:
PHP Code

$posts['POST_DEFAULT_BODY'] = str_replace("%% GRAEMLIN_URL %%",'graemlins/default',$posts['POST_DEFAULT_BODY']);

Note: this board is replacing
Code
%% GRAEMLIN_URL %%
, so i put spacing there. remove the spaces when you add the code..