I can't quite remember FoBoT, and am not currently at a DF "enabled" computer.
It's really simple though. Just open up the bz2 file and take a look. If I remember correctly only the first couple of lines have standard text info (the rest is all numbers). The handle (if it's in there (I can't remember)) will be in those lines.
However the handle does appear in the name of the file, and obviously as well in handle.txt.
You could upload somebody else's structs by copying over their files (including filelist.txt) and handle.txt and running the client. That's just an educated guess though.
Could we get a confirmation?