What about using Google Cloud Shell (https://cloud.google.com/shell/docs/; free, open to anyone with a Google account) as a jump host to your servers? Or using GCE's ssh-in-the-browser feature (https://cloud.google.com/compute/docs/ssh-in-browser) to connect to your own GCE VM (not free, in this case) and using it as jumphost?

Both Cloud Shell and SSH-in-the-browser use an in-browser SSH client, so the connection is encrypted all the way and not MITMable.

p.s. full disclosure: I work at Google on the team that maintains both of the above.