Handling unsupported asset bundles

It looks like when you try to load an asset bundle in Unity 4.2 that was built in a previous version of Unity, via the WWW.LoadFromCacheOrDownload method, will cause a fatal error in Unity Editor on Windows and freeze Unity Editor on Mac OS X.

The Unity 4.2 release notes state:

Asset bundles built in prior versions of Unity are no longer compatible with Unity 4.2 (this has been necessary because of changes to how built-in resources are handled).

However, is there any way to gracefully handle unsupported asset bundles when loading them into cache?