Can I disable IdentityFile?

[M Rubon]

I would like to ensure that I connect with mysever only using a
specific agent and never an IdentityFile.  (It turns out that I had
accidentally been authenticating using one of the implicit
IdentifyFile locations in .ssh)

I want my imaginary ssh configuration to be the equivalent of
host myserver
    IdentityAgent /tmp/agentformyserver
    IdentityFile never

I have tried setting an explicit "IdentityFile /dev/null" and
"IdentityFile /tmp/id_rsa_IGNORED".  Ssh then ignores the
IdentityAgent and fails because the IdentityFile is empty or
rightfully not recognized by myserver.

Is there another way to do this?

M