Custom build backend, stop build making {source}/dist directory

[squarris]

I'm trying to create a package for my project. The first thing I want to do is redirect all build artifacts to a custom directory. I know I can supply --outdir however my build directory needs to be generated as part of the build process so I can't supply at the command line. I can write a custom backend to redirect but the build still makes the {source}/dist directory in _call_backend before calling _handle_backend and so i cant stop it.