After one unsuccessful attempt and one hack-ey successful one, getting FreeBSD up and running on GCE is now a one-liner:
$ gcloud compute instances create pandora --image freebsd-10-2-release-amd64 --image-project=freebsd-org-cloud-dev
$ gcloud compute ssh agam@pandora
... and that's it. Kudos to whoever made this happen!
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