playing with smartcard: rsa key upload?

[Andreas Hasenack]

I began playing with smartcard support and enabled this in openssh-3.5p1
on linux.

The -U (upload) option unfortunately doesn't work yet with ssh-keygen:
$ ssh-keygen -U 0
Enter file in which the key is (/home/user/.ssh/id_rsa): 
key uploading not yet supported

Is there a tool to upload an openssh rsa key to a smart card so that I can
use it with ssh -I later on? Should I just upload it as a regular file?
Any pointers to some documentation explaining how to do this with openssh?