This won't work from the file with the same name as the xql, because db_qd_get_fullname requires a certain level between it and that file. If you do want to use it directly, pass a 0 as the second parameter so that it can uplevel to the right place. Example:
set full_statement_name [db_qd_get_fullname $statement_name 0]
set sql [db_qd_replace_sql $full_statement_name $pre_sql]
Of course, the db_map option is probably a better one.
paul