I make the ugly mistake of upgrading without taking a snapshot. But I got lucky. I had a second OSX VM on my VMWare ESX 5 host. I added the 10.7.2 disk to the other OSX, booted and replaced the offending extension. A bit painful (specially to admit that I forgot the snapshot) but quick. Now I have both OSX images at 10.7.2 and I've saved the ext on a tar file for future use.