Microsoft recommends using Sharepoint, and that seems to be what they expect: http://msdn.microsoft.com/en-us/library/ee637439.aspx

http://msdn.microsoft.com/en-us/library/hh231687.aspx

You can also just send the powerpivot files over as these are Excel files: http://msdn.microsoft.com/en-us/library/ff628113%28v=sql.100%29.aspx