Why not just keep using a little script? GCE comes with gsutil
installed, which you can use to transfer files to GCS. Try this:
passthru('gsutil cp '.$filepath.' gs://bucket/', $status_result);
Note that, for auth to work, you'll have to make sure your instance's service account is scoped to access GCS, see: https://cloud.google.com/compute/docs/access/create-enable-service-accounts-for-instances#changeserviceaccountandscopes