Is there a clean way to pass custom options for a transformer?

I have created a couple of custom transformers for React Native (e.g. https://github.com/kristerkari/react-native-css-transformer).

Is there a clean way to add custom options for a transformer? So far I haven't found a way. I could always wrap the transformer and extend the options object, but it would be nice to have a way to do it from rn-cli.config.js.

Currently I can only add the extensions and the module/filename of the transfomer:

module.exports = {
  getTransformModulePath() {
    return require.resolve("react-native-css-transformer");
  },
  getSourceExts() {
    return ["css"];
  }
};

Start with the rn-cli.config.js entry points getTransformModulePath() and getSourceExts(), then trace how Metro passes configuration to custom transformers. Define completion as allowing transformer-specific options to be supplied from rn-cli.config.js without requiring a wrapper, with coverage for the documented configuration behavior.