So far, no reply.
Since posting, I've read a comment that said one could patch the video driver so that it would install into an available, empty resource tranche rather than failing through the lack of M/B arbitration.
This at least seems plausible but I have no idea how to do it. Where the driver tries to locate its' installation code is easily findable from Devices Manager by Resources Connection PCI Bus. Changing that to unused resources is the challenge, I guess.