I ran into this importing to PowerPivot too.
You can just store in SQL as Date datatype as needed, but in the query, Cast to Datetime on the way into Excel.
CAST(YourDateColumn as DATETIME) as YourDateColumn
Then just format the column in Excel as needed (f.e., "MM/dd/yyyy"). This way, you get the compact storage in SQL, and also take advantage of the native datetime features in Excel.
Hope that helps.
Brent Greenwood, MS, MCITP, CBIP // Please mark correct answers and helpful posts // http://brentgreenwood.blogspot.com