Set default disk space using curlftpfs

Question

I have setup curlftpfs for my remote ftp server. I'd like now to tweak it a little and set the actual disk space available instead of the default magic number used (7.5T):

# df -h
Filesystem                                              Size  Used Avail Use% Mounted on
[...]
curlftpfs#ftp://hd1.freebox.fr/Disque dur/              7.5T     0  7.5T   0% /media/freebox

This way I'll have a better view of what disk space is actually left, before shooting myself in the foot.