UnionFS-like filesystem for windows

I'm looking for something that works like UnionFS in Windows 7. My usecase: having clean code working directory in a read-only directory, and compiling it in a union filesystem which would store compiled binaries logically in the same place, but physically in different directory.

Libraries do not work this way, even though they were accepted as an answer in UnionFS alike on windows, Virtually merge folders -- they only show top-level directories in one place.

The code itself is huge (2GB of data), and I'd like to avoid copying it for every build in my build server.