I chatted to a colleague who gave me this answer. It is possible, but not advisable.
To install an alternate package:
- Open Synaptic Package Manager
- From the menu select Settings | Repositories
- Add the alternate source (in my case the maverick repo)
- You should be prompted to reload sources, if not hit the Reload button
- Find and select the package to downgrade
- From the menu select Package | Force version...
- Pick the older version
- You will be warned that this may cause dependency errors
- If you're feeling brave, go ahead
Reverting would involve undoing this process. In my case this involves dealing with a broken video driver, and that sounds like a nightmare, so I'll just wait for the bug to be fixed.