Thanks @hicksd8, but alas this is all virtualised.
How Packer works; in a nutshell, it will create a temporary VM, attach the connect extra media like a floppy or cd-drive (these are all virtual devices), and then boot from CD and install. Once its done, VMWare takes a snapshot, converts a template, and destroys the VM.
To be honest, whether or not its Virtual is probably academic because the problem is the same; I can't modify the ISO, so I need to boot from floppy, with a custom AI Manifest, then continue installing via the mounted ISO.
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Thanks @Peasant - I will take a look.
This could be a good starting point. I'll be sure to report back with how it gets done.
Thanks,