You can use the -U option (--database-root PATH)

updatedb -l 0 -U /home/user/music -o /home/user/databasefile

-o writes to the output file

-l 0 makes that you can read it, otherwise it is only accessible for locate

Then you can then use it like:

locate -d /home/user/databasefile Dylan

-d sets the databasepath

To use mlocate with more than one root directory, simply create two databasefiles, and use locate with two databasepath's options like this:

locate -d /home/user/dbfile1 -d /home/user/dbfile2 searchstring

To sum it up and answer the question more specific:

updatedb -l 0 -U /home -o /home/user/home_dbfile

updatedb -l 0 -U /data -o /home/user/data_dbfile

locate -d /home/user/home_dbfile -d /home/user/data_dbfile Dylan