Here is a link to earlier in the thread with the instructions:
https://discussions.apple.com/thread/2384136?answerId=13097053022#13097053022
Personally Kext Helper bricked my mac after its scripts totally messed up my /System/Library/Extensions directory, so I just moved the files into place myself.
Make sure you have a Time Machine backup before you do this, and look up ahead of time how to boot your Mac in safe mode if you screw this up. You are messing with system files. Don't do this if you don't know what you are doing. Do this at your own risk. Et cetera.
I backed up the 10.7.4 kexts first:
mkdir -p ~/kexts/10.7.4
cp -a /System/Library/Extensions/ATI*.kext ~/kexts/10.7.4/
I unzipped the 10.6.2 kexts and put them into ~/kexts/10.6.2, then copied them and fixed up ownership and permissions by hand (which is pretty much all Kext helper does):
cd ~/kexts/10.6.2
sudo cp -a ATIFramebuffer.kext ATISupport.kext ATI2600Controller.kext /System/Library/Extensions/
sudo chown -R root:wheel /System/Library/Extensions/ATI*
sudo chmod -R 755 /System/Library/Extensions/ATI*
As in the original instructions, replace ATI2600Controller.kext with the appropriate driver for your system. I think I also did ATIRadeonX2000.kext, but I don't remember.