Currently I have mostly-useless commands in my Dockerfile like
ADD stuff /docker_setup
RUN /docker_setup/install.sh && rm -rf /docker_setup

This is ugly. Can we have:
BIND_CONTEXT /docker_context
RUN /docker_context/stuff/install.sh

I'm not picky about the syntax. I want to have docker build do what docker run -v does, but during the build process.