How to add binary dependencies for bundlerEnv

I've been trying to add some binary dependencies to a gemset I'm passing to bundlerEnv. The gem itself contains a binary extension component which requires a specific native library to be present.

I can't seem to find the bundlerEnv definition though and the docs have only pure-ruby examples. How would I add a dependency on some libfoobar (available in nixpkgs) to gemset entry like:

  foo = {
    dependencies = [];
    gem_platform = "ruby";
    groups = ["default"];
    platforms = [];
    source = {
      remotes = ["https://rubygems.org"];
      sha256 = "...";
      type = "gem";
    };
    target_platform = "x86_64-darwin-21";
    version = "1.2.3";
  };