This may require changes to metal3-dev-env. For local bond testing I have been hacking metal3-dev-env with the following change:

diff --git a/vm-setup/roles/common/defaults/main.yml b/vm-setup/roles/common/defaults/main.y
ml
index 1d725ef..6d36e3d 100644
— a/vm-setup/roles/common/defaults/main.yml
+++ b/vm-setup/roles/common/defaults/main.yml
@@ -80,4 +80,4 @@ external_network:
          addr: "{% if baremetal_network_cidr_v4|ipv4 != False %}127.0.0.1{% else %}::1

"
      srvs: "dns_externalsrvs | default([])"
 
-networks: "{{ provisioning_network + external_network }}"
+networks: "{{ provisioning_network + external_network + external_network }}"

This gives us two nics on the external network that we can bond. However, this is obviously not a general solution so we need to figure out if we can define the networks list in dev-scripts (probably vm_setup_vars.yaml) or if we will require support in metal3-dev-env to do this.