I've just found a way to sort this problem out that gets around this install 'problem':
In order to get these to show and also to have access to all the other georgeous 422 codecs and other goodies, download the new QT codec pack: http://support.apple.com/kb/DL1396
Then use the little app UNPKG ( http://www.timdoug.com/unpkg/ ) to unpack the contents by simply dragging the downloaded PKG codec pack onto the app window. This then unpacks on the desktop. Inside navigate the folders until you get to the QT .component files.
Next, drag these into your Library/Quicktime/ folder and then you'll have the LT codecs ( and many others) to use in FCP 6 and all other apps like Streamclip, QT Pro etc. (I would recommend renaming the existing ones in case of problems of course)
I've done a test with it and it works like a charm on my Mac Pro running 10.6.7 and FCP 6.0.6. I'm not able to create an LT sequence but if you create a new one and then drag the material on with the prompt enabled to match settings it will make an LT sequence. I was also able to render out a 422 LT clip from QT Pro and Streamclip to use in the project. All the correct 422 labels also show in the codec lists in all encoding apps.
If you try and install the QT pack on anything not FCP X it will give you an error but this manual installation gets around the Apple Police and their insistence you buy everything new the minute it comes out! You can keep FCP 7 and X, I'm quite happy with 6!