How do I/can I use before-script-linux to install external dependencies

[denehoffman]

I have a PyO3 library that needs MPI and clang to be installed on the system prior to building. I can do this fine for my MacOS builds, but linux builds via manylinux execute through a docker image, so I'm trying to figure out how I'm supposed to inject these dependency installs into those build pipelines. I've tried it a few ways and nothing is working, any tips?