You could try using the OCL (Open Core License) version of the Catalyst driver.
I'm not an ATI user so I've had little experience with their drivers.
I had the same issue with a friends Dell laptop HD 5470M graphics.
(Dell offers a 1 yo driver and any driver from AMD just doesn't install and leaves you with Standard VGA driver after reboot)
Same problem with another friends Toshiba laptop with 5430 had the exact same problem trying to install current Catalyst driver.
I used ocl versions of the Catalyst driver and they installed and worked in the above 2 instances.
I think the problem is that the laptop Manufacturer doesn't wan't to pay for license fee for every newer version video driver that needs compatability testing and driver signing so they don't give permission for AMD to add their Manufacturer/Vendor ID to the driver inf.
Hence the laptop manufacturer release their laptop with a driver they offer and then they never seem to update the video driver for their laptop after that.
It may also be that the laptop manufacturer prefers to handle driver updates themselves so they aren't swamped with customers bitching that the current driver doesn't work properly with their brand of laptop.
Either way it always boils down to manufacturers just don't want to spend more money on keeping their customers happy with the old product that they have already taken your money for.
They want the customer to spend more money on a newer version of their laptop to keep the manufacturer happy.
I found links to current AMD/ATI Catalyst Mobility 11.12 WHQL OCL drivers here: http://www.nsaneforums.com/topic/110...catalyst-1112/
But I haven't tried any of these at all, so I can't say if they will work or not.
Drivers I tried were 11.11 from some other site I found through google.
(11.12 weren't out when I installed on my friends laptops)
Oddly I can't seem to find OCL reference at AMD website at all when I search.
Hope it helps, if not then hacked inf file can achieve what your after, but that's upto you to work out.