I would do so by using MS Access and LINKing (not importing) in the Excel spreadsheets, then creating a UNION ALL query within Access to create a datasource for Crystal to use, as in:
select 'WKS1' DataSource, * from wks1
UNION ALL
select 'WKS2' DataSource, * from wks2
Now you have both sets of data and a column designating it's source.
-k