You can build a tool using the SDK or buy a third party tool like Scribe (www.scribesoft.com).
Link to SDK:
http://www.microsoft.com/downloads/en/details.aspx?FamilyID=420f0f05-c226-4194-b7e1-f23ceaa83b69
The data import wizard has taken on some of the functionality of the migration manager.
http://www.powerobjects.com/blog/2010/10/01/crm-2011-data-import-wizard/