No, it isn't possible. And looking back at this method getKnownHosts() I really wonder what use it is and why we wrote it.
The good news is, I've added 2 new methods.
public String[] getKnownHostnames() // to get a list of the host names in known_hosts
public SSHFTPPublicKey[] getKnownHostKeys(String hostname) // to get the public keys stored for this hostname
It'll be released as part of 3.0.1 later today - email us if you want to try it out now (support at enterprisedt dot com).