User-defined environment variables in z2jh

Is there a good way to propagate user-defined environment variables to kernels in a z2jh-based deployment? Users can set their own variables (such as personal API keys) in a .bashrc file, which makes them available in terminals, but these are not inherited by kernels.

I could imagine a new entry point Spawner.cmd that tries to source a .bashrc after mounting the user volume, but before launching the notebook server, but this seems a little brittle to me.