this is done Using Ray Adams ATI Tray Tool utility . The advantage of doing it the alternate way is that the Nvidia card check is bypassed and you get ingame AA rather than AA forced by the display driver. Big deal you are probably thinking but the ingame AA is faster as it isn't done via brute force.and more importanly you cheat nvidia
my system specs..win7 32 bit,ati 5770,catalyst 10.6,batman game version 1.0
2nd-Create three different profiles in the ATI Tray Tools app, one for the BmLauncher.exe and ShippingPC-BmGame.exe,BmStartApp.before saving,
In the 'Direct3D Tweaks' option, enable the tickbox to change the adapter identification
In the Vendor ID put 10DE for the Device ID put 5E2 .it resembles NVIDIA GeForce GTX 260 . Do this for both profiles saving each one before starting the next.