Hey HC_andy,
Why not put ESXi directly on a VM running on ESXi?
To do that first go to your browse and then type to https://your-esxi-ip-here/mob/?moid=ha-host&doPath=capability and look for NestedHVSupported. If it says true, then you can install the ESXi on your VM after Checking the HV tab like shown below
Let me know if you need more info. Would be glad to help you.