There is no way to convert a LUN, which is block storage, to a CIFS share, which is file storage. LUNs are seen as large files by the storage system. Shares are simply gateways into flexible volumes.
The only way to do this is via file-based migration, such as robocopy:
http://technet.microsoft.com/en-us/library/cc733145.aspx
This would be done from a Windows server that has the iscsi LUN mounted and CIFS share also attached. I'd recommend using copy and not move, as you don't want to get stuck in a bad place if something happens during the migration.
