1. Create FILESTREAM filegroup.
2. Add FILESTREAM column to table
3. Choose one of:
a. Write an app to select data from the BLOB column and stream it into the FILESTREAM column
b. UPDATE <table> SET <filestream_column> = <blob column>;
4. Drop blob column
Note: Filestream data is in a separate filegroup, so you can selectively back up all the other filegroups.