Adding disk space to an FTP directory -- ideas?

[Greg Brooks]

I currently use most of /var for a depository of files that move in and
out via FTP. /var runs on a secondary hard drive in the system, along
with a partition called /storage that's currently empty.

Only one user ("ftpuser") has login rights to the ftp system, although
it's not jailed with its own /bin directory, etc.

The question: How do I take the available space in /storage and make it
available to the ftpuser? Adding a symlink to /storage within the FTP
area doesn't seem to work.

Any help much appreciated.
G.