You could setup a PXE server an host all of the versions of ESXi you need. Also, I am not 100% positive but you may be able to use Auto Deploy from a host running 6.7U1, I am just not sure if you can deploy older versions of ESXi
there are several "multiboot" tools available that allow to copy multiple ISO files to a USB drive and to pick one of them to boot from via a menu (e.g. XBoot).
Here is a starting point: https://www.pendrivelinux.com/tag/boot-multiple-isos-from-flash-drive/
Is this what you are looking for?
Thanks a lot. Yes i was looking for something like Xboot. I have tried it and did some tests with my HPE server.
Even though XBoot does not support UEFI boot endnu, but it works find with legacy BIOS...
Thanks once again.