The following works for us against an ASA DB:
Long ll_return
String ls_lName, ls_fName
DECLARE sp_local_proc_name PROCEDURE FOR dba.sp_stored_proc
@a_lName = :ls_lName,
@a_fName = :ls_fName,
@a_return = :ll_return OUTPUT;
EXECUTE sp_local_proc_name;
IF SQLCA.SQLCode = 0 OR SQLCA.SQLCode = 100 THEN
FETCH sp_local_proc_name INTO :ll_return;
END IF
There is also a way to do it without the OUTPUT parameter, using a SELECT at the end of the stored procedure.