Just add new line for options database:
if ( isset( $tables['usermeta'] ) && defined( 'CUSTOM_USER_META_TABLE' ) )
$tables['usermeta'] = CUSTOM_USER_META_TABLE;
if ( isset( $tables['options'] ) )
$tables['options'] = $blog_prefix . 'options2';
where options2 represents the new database (ex: wp_options2)
