IIRC, the SINGLE_BLOB option returns the data as single-row, single-column value of type varbinary(max), and when using OPENROWSET to import LOB data that exceeds 8,000 bytes in length, you have to use a format file to specify the maximum length of the data. See here for more:

http://msdn.microsoft.com/en-us/library/ms178129(SQL.90).aspx