I think this is a 'do you really want to do this (*)' kind of thing. Excel has it's own formatting rules. If the file is small enough to 'fit' in excel, it's probably a config file, which tend to be really really format sensitive. I don't think excel has the concept of a BLOB, just a stream of bytes that aren't interpreted.
Also, you'll probably have to deal with locking and copying problems.
I suggest sqlite. sqlite3 can do BLOBs. And there are so many interfaces to it, including most programming languages, and small guis. Excel/OpenOfficeCalc could access sqlite3 with the right DB drivers. Your DB, like the excel file, would just be a file on disk someplace, you don't need to set up a db server.
(*) yes i hate 'do you really want to do this' posts too.