I'd love to know how STD got VVRAM working just out of curiosity, also it's a bit of bad form not to let the VA developers into the secret.
It can't be the old BandLimit hack I'd have thought as that doesn't work on RiscPCs (might have on RO3.7). Maybe STD found a way to make VARPC-SE enable RedSquirrel's ARM7500 emulation.
Other than that I can only think of a hack to RO4. I'd be particularly interested if they've got it to make use of the GF4 acceleration, or just allowed bigger/more colourful modes which the GF4 just happens to support.
The person who bought a PC thinking it was a hardware RISC OS machine - was he actually misled intentionally or just uninformed about things RISC OS?