Warning: Here be Dragons. I managed to restore the needed apps without bricking my tablet. If you mess this up, you won't have a working tablet and Lenovo probably will not flash it for you.
First:
You can get a copy of the 75US /system here:
http://www.thinkpadtabletforums.com/thinkpad-tablet-root-hacks-mods-and-development/ota2-us-released...
Second:
Make a backup of root using OTA Rootkeeper
Third:
To restore, all you have to do is copy that system folder onto your /system folder. My root was acting up and kept remounting /system as ro once a second, so I needed to copy using an adb shell over USB. You may have better luck than I did with root explorer or ES.
It may be possible to just run the preinstall apk. I also had issues replacing things in /system while running, but I managed to finish the copy and reboot before the tablet shut down. If you're careful, you could probably load fastboot or something to copy while /system is not mounted.
Forth:
Tempoarily disable root and apply OTA2
Fifth:
Restore root and check that it works.
Sixth:
Temporarily disable root and apply OTA 2.5
Seventh:
Restore root and check. You should be fully updated with root.
I decided I'm going to leave the stock apps this time. We're 2 to 3 months from ICS, and I really want that update. Since Lenovo doesn't release full, signed images, it's very likely you can get in a position where you cannot update.
) (same here)
