[horde] Restrict SSH2-VFS to an user-depended path

[Steffen]

I have configured Gollum to use a ssh2 backend. With

$backends['ssh2']['root'] = '/home';
$backends['ssh2']['params']['timeout'] = 20;

I can restrict the top level to /home on the server. Is there a way to 
limit the top directory (VFS root) to the home of the user currently 
logged in? That is either, dynamically, the directory the user got right 
after the first login or, statically, /home/<account> ?

Mostly I want to deny (easy) access to /home and some other paths not 
only because of security, but also because the PHP SSH implementation 
stalls when entering such directory and never gets a timeout.

Kind regards,

-- 
Steffen