The "copy" command can take "scp:" as a source protocol, just like "tftp:" or "ftp:" among others. You'll need to specify a server running SSH that supports SCP (and specifically SFTP is not an option), but that should be common place for any SSH implementation on most Linux or Unix machines (should work with Cygwin or SecureFX on Windows too).
Not sure about using another router as an SCP server. My own experience using the SCP server option found it to be quite picky. Didn't work with any SCP client on Windows except PuTTY (pscp.exe). A brief test between a couple of 3845s running 12.4(15)T9 never yielded a working result, via local or tacacs.
Hope that helps,
Justin White
CCIE #14745
