At about line 91 
----FIND---- 
unset($input['input']);
unset($input['not_unset']);
while (list($var,) = @each($input)) {
if (!in_array($var, $not_unset))  { 
unset($$var); 
} 
}
unset($input);
} 
----REPLACE WITH---- 
	   unset($input['input']);
   unset($input['not_unset']);

   while (list($var,) = @each($input))
   {
      if (!in_array($var, $not_unset))
      {
         if ($var=="option"){
         }    elseif ($var=="Itemid") {
         }    elseif ($var=="id") {
         }    elseif ($var=="task") {
         }
		 else {unset($$var);} 
      }
   } 
   
   unset($input);
} 


---- at approx. line 248 ---- 
---- FIND ---- 
$query = "SELECT id FROM " . $mosConfig_dbprefix . "menu WHERE link = 'index.php?option=com_forum'";
 $db->sql_query($query);
 $Itemid = $db->sql_fetchfield('id');

----REPLACE WITH----
//$query = "SELECT id FROM " . $mosConfig_dbprefix . "menu WHERE link = 'index.php?option=com_forum'";
//$db->sql_query($query);
//$Itemid = $db->sql_fetchfield('id');

Much thanks to Alkor from TIM_online for help here.

PhpBB here normally throws out the variables here, this will mess up your frontpage when you include common.php. This hack prevents PhpBB from dumping the values of option and Itemid. I've yet to see any major negative effects from these edits, as they are necessary to get this working, but I am not 100% sure that they won't affect something else. My site has been running fine for a few months, so I think we're okay.