ssh -F /dev/null root@hostnameworks, but this wasn't working with ssh-copy-id.
Turns out that the ssh-copy-id script is braindead and only expects one or two (with the 1st beginning with -i) arguments.
lo and behold, some single quotes did the trick:
aelwell@pcitgtelwell:~$ ssh-copy-id '-F /dev/null root@concerto'
Are you sure you want to continue connecting (yes/no)? yes
Now try logging into the machine, with "ssh '-F /dev/null root@concerto'", and check in: ....