If we made it so that all hosted accts have a shared group. We could add a "Match" line to match just the hosting groups, and then add "AuthorizedKeysFile" line.
This would force all hosting ssh accounts to use imscp loaded ssh keys, while leaving the rest of the accts on the server (i.e. admins, etc) to use ~/.ssh/authorized_hosts and ~/.ssh/authorized_hosts2
For instance (just a sample):