root@telekomander:~# grep usb /etc/opkg.conf 
dest usb /usb/
root@telekomander:~# opkg -force_space -dest usb install libopenssl
Installing libopenssl (0.9.8i-3) to usb...
Collected errors:
 * Only have 1056 available blocks on filesystem /usb/, pkg libopenssl needs 1258
root@telekomander:~# df -h /usb/
Filesystem                Size      Used Available Use% Mounted on
/dev/scsi/host0/bus0/target0/lun0/part1
                        465.2M     10.5M    430.6M   2% /usb
root@telekomander:~#