I've not had to do this for a while but I always used a UNION in my SQL with a default size for the field:

(There are no records in DummyCursor)

Select 00000000.000 As Result From DummyCursor ;
Union
Select field1 * field2 * field3 As Result From RealCursor ;
Into Cursor Result

If you have lots of fields in the output, then it can become annoying having to specify them all in the first section of the query, but it should achieve what you are after.