Looks like I was somewhat optimistic. From the “GPU workers” doc:
Adding GPU workers with GCP
Google supports GPUs slightly differently to most clouds. There are no GPUs included in any of the default instance templates, and therefore they have to be added manually.
To begin, add a new machine with Juju. Include any desired constraints for memory,cores,etc :
juju add-machine --constraints cores=2
The command will return, telling you the number of the machine that was created - keep a note of this number.
Next you will need to use the gcloud tool or the GCP console to stop the instance, edit its configuration and then restart the machine.
Once it is up and running, you can then add it as a worker:
juju add-unit kubernetes-worker --to 10
…replacing ‘10’ in the above with the number of the machine you created.