Matt, I just applied your patch + a few modifications. To workaround the problem of -base not being loaded and initialized before -corebase I simply stopped using @"", even on objc source files. Currently, only the identifiers defined in Identifier.m are NSConstantString objects, which may or may not cause other problems. I was able to run the test suite without getting massive failures; there are still a few but they were there before.
Let me know if the latest svn works for your needs.