I dont know how much help this would be to you but I'll give you a "raw code" that you can play with:
edit index.php, find:
PHP Code:
eval("\$forumbits .= \"".gettemplate("forumhome_forumbit_level$depth$tempext")."\";");
if ($depth<$forumhomedepth) {
$forumbits.=makeforumbit($forum['forumid'],$depth+1,$forumperms);
Replace it as
PHP Code:
if ($forum[forumid]==A) {$forumhomedepth_log=X;$depth_log=Y;}
elseif ($forum[forumid]==B) {$forumhomedepth_log=Z;$depth_log=W;}
else {$forumhomedepth_log=$forumhomedepth;$depth_log=$depth;}
eval("\$forumbits .= \"".gettemplate("forumhome_forumbit_level$depth_log$tempext")."\";");
if ($depth_log<$forumhomedepth_log) {
$forumbits.=makeforumbit($forum['forumid'],$depth_log+1,$forumperms);
Now play with A, B, X, Y, Z and W and you'll see how it works..