You will have to drop the existing index and then create the index with the INCLUDED columns
The link below can help you with the syntax to create the index with INCLUDED columns
http://msdn.microsoft.com/en-us/library/ms190806%28v=sql.90%29.aspx
How to post data/code on a forum to get the best help - Jeff Moden
http://www.sqlservercentral.com/articles/Best+Practices/61537/