Copy the keys LayoutID and PathMapRef (they're inside key Layouts) to AppleHDA.kext/Contents/Resources/layout??.xml (replace original contents or create a new file if it doesn't exist, ?? = LayoutID);
Copy the dict from key HDAConfigDefault (it's inside key HDA Hardware Config Resource) to key HDAConfigDefault in AppleHDA.kext/Contents/PlugIns/AppleHDAHardwareConfigDriver.kext/Contents/Info.plist (paste as child);
Use to edit the plist files.
If the codec isn't ALC889A or AD1988B you will also need to edit the file AppleHDA.kext/Contents/MacOS/AppleHDA (binary).
For Realtek (ALC88x) replace the 4 instances of 85 08 EC 10 (inverted bytes of codec 0885 and vendor 10EC) by your codec, for example, 88 08 EC 10.
Use an hex editor ( ) or the command
sudo perl -pi -e 's|\x85\x08\xec\x10|\x88\x08\xec\x10|g' /System/Library/Extensions/AppleHDA.kext/Contents/MacOS/AppleHDA
sudo perl -pi -e 's|\x8b\x19\xd4\x11|\x9b\x98\xd4\x11|g' /System/Library/Extensions/AppleHDA.kext/Contents/MacOS/AppleHDA
If you have a patched AppleHDA for Snow Leopard (10.6.7 or older), instead of taking values from LegacyHDA you will get them from AppleHDA plug-ins.
CommonPeripheralDSP, PathMaps, LayoutID and PathMapRef come from AppleHDA.kext/Contents/PlugIns/AppleHDAPlatformDriver.kext/Contents/Info.plist
The dict in HDAConfigDefault comes from AppleHDA.kext/Contents/PlugIns/AppleHDAController.kext/Contents/Info.plist
Snow Leopard 10.6.8 AppleHDA has the same structure as Lion one.