Probably easier to do it manually, but here's an idea to do it automatically.
Imagine you have a Vagrantfile which defines a number of nodes for your microk8s.
Instead of doing the following,
vagrant up node-01 ; vagrant up node-02 ; vagrant up node-03 # etc. from the host
What if you could do,
SEED=startup-script
OUT=$(vagrant up node-01 -c "./${SEED}")
OUT=$(vagrant up node-02 -c "./${OUT}")
etc. (Run a command inside your VM, and save the output to a variable and then reuse it for subsequent calls).
You would need to inject a startup-script inside your nodes, but then in essence you'd be writing a wrapper script which runs the "vagrant up node-X command".