I guess that no one that read this has tried this before, or I am asking the wrong question (seems more likely than it not being possible).
In lieu of some clarification via this thread or the ticket I raised, attached is my xml file for the GreenWave Reality Inc. GWPN5 Multi-socket PowerNode (5-plug) in case there is anyone else using this device.
This includes endpoints for all 5 sockets. I also removed the switch and meters for endpoint zero as they were just duplications of endpoint/socket 1.
You can add it manually following these instructions (replace ESH-INF with OH_INF)
gwpn5_0_0.xml (10.8 KB)