OS X USB installer utilities, cannot ssh any host

I booted my mac from a OS X USB key intaller. I cannot boot it from HD because OS is damaged.

I want to copy some file from my Mac to another computer with scp.

The problem is that the installer is a read only volume and ssh cannot add the RSA key of the host I want to connect to to the /var/root/.ssh/known_hosts file, not even with root. It prompts for password but the STDIN seems to be blocked.

Is there a way to circunvent this?