That's not strictly true.
Firstly some Twonky settings are exposed in Twonky web UI at http://mybook\_ip\_address:9000
Secondly you can SSH in. Load the Mybook UI go Settings > Utilities > Import / Export Current Configuration
Export the current configuration, open the file in notepad (Wordpad screws the formatting so be careful), find the bit that says: ssh_enable="disabled", change to ssh_enable="enabled", save the file
Now back in the Mybook UI go Settings > Utilities > Import / Export Current Configuration and import the file you have just saved. The Mybook reboots and hey presto SSH is enabled.
On mine the login was root / welc0me (that is welcome with a zero instead of an oh).
Be careful as I imagine you will not be supported in any changes you make....