It is not a software limitation. Those ROPS/shader sectors are physically disabled. Usually laser cut the connections for those blocks in production. There is no way to undo that.
I see your point and then i don't. I took the cooler of cleared the thermal grease up and compared the chip with a regular chip of a 5870. Looks exactly the same, no laser cuts of any kind I could see.
If the chip was done this way on purpose without any chance of messing with it, why in the world would it need to be on a 5870 PCB and not on a 5850 or even a new one. There has to be some sort of magic to get something going. I just refuse to believe that is it. The sad thing is you can't find anything about those cards useful anyway on any message board. It seems people are so shocked by the price preformance that they don't even try.
There used to be smart people on forums who figured stuff out like that came up with modified bioses ect...
I really wonder what is going on with that card. There might be nothing but a chip to chip comparison shows the exact same chips layout and chip then on a 5870 without any cuts. I might be chasing a ghost here but you never know until you have used all your options.