Consider using plain old scp program, which has (at least in recent OpenSSH) special command line option (-i) to specify your custom identity (private or secret key).
hmm... not a bad idea. I'll look into that. Of course I have to make that private key world-readable (uh, gives me a bad feeling - but not worse than putting passwords into scripts I guess) or have it chowned. I wish I was root on that machine...