I suggest you read these 2 links

http://consultingblogs.emc.com/jamiethomson/archive/2006/12/20/SSIS_3A00_-Using-stored-procedures-inside-an-OLE-DB-Source-component.aspx

http://social.msdn.microsoft.com/Forums/en-US/sqlintegrationservices/thread/e8645006-899a-40bb-b144-6d65ee0a6290/

So the real challenge is getting the data out of the stored procedure. You could build a work table and then

INSERT INTO dbo.WorkTable

EXEC dbo.StoredProcedure

Then you can SELECT columns FROM dbo.WorkTable to feed your data into an SSIS data flow and then flow that down to an Excel destination.