Here's a clean override that implements the routes config and redirectTo() method into controllers for ExtJS. It's compatible with the same syntax used in Sencha Touch but with one extra app-level option (see below) for efficient ExtJS initial rendering. I was able to do it with a lot less code than ST2 uses by weeding out all the ST1 routing artifacts littering it.
Download locally or use right off GitHub:
suspendLayoutUntilInitialRoute: true, // true to suspend layouts during app startup until initial route is handled