You could create a query like this (and give it any name, I will use "Query1" for this example.:
Code:
SELECT Stuff1, Stuff2, Stuff3, 2 As Sort1
FROM Stuff
UNION ALL
SELECT Field1, Field2, Field3, Sort1
FROM Fields;
You can then create a query off of this query.
Add all the, including the SORT1 field.
Then uncheck the "Show" box under the SORT1 field, but select the "Ascending" sort option under it.
Then it will include this field in your sort, but not your export if you export this second query.