Crossover will follow symlinks in ~/.cxoffice to discover bottles you've moved to other locations. Sometimes this is done for large game installs that a user wants to locate on an external drive with more space. The partition containing the bottle needs to be an ext3/ext4 filesystem.

What you want to do is move the entire bottle directory (located in ~/.cxoffice) to its new location, and then symlinking the new location to the old.

For example:

$ mv ~/.cxoffice/Steam/ /media/externaldrive/

And then symlinking back to the old location where Crossover expects to see the bottle:

$ ln -s /media/externaldrive/Steam/ ~/.cxoffice

To do this in the future with new installs you'll need to create a blank bottle for the app first, then move the bottle over the external drive, symlink, and then perform the installation of the program into that bottle.