You could just hard-code the link:
/includes/modules/sideboxes/YOURTEMPLATE/information.php
Code:
// Forum (phpBB) link:
if ( (isset($phpBB->phpBB['db_installed_config']) && $phpBB->phpBB['db_installed_config']) && (isset($phpBB->phpBB['files_installed']) && $phpBB->phpBB['files_installed']) && (PHPBB_LINKS_ENABLED=='true')) {
$information[] = '<a href="' . zen_href_link($phpBB->phpBB['phpbb_url'] . FILENAME_BB_INDEX, '', 'NONSSL', false, '', true) . '" target="_blank">' . BOX_BBINDEX . '</a>';
// or: $phpBB->phpBB['phpbb_url'] . FILENAME_BB_INDEX
// or: str_replace(str_replace(DIR_WS_CATALOG, '', DIR_FS_CATALOG), '', DIR_WS_PHPBB)
}
becomes:
Code:
// Forum (phpBB) link:
$information[] = '<a href="' . "http://mysite.com/phpbb2/index.php" . '" target="_blank">' . BOX_BBINDEX . '</a>';