Set and activate default conda environment

Using conda-shell installed via

environment.systemPackages = with pkgs; [

how can a user configure and activate a conda environment (other than the base environment) as the default when calling conda-shell or have a custom conda-shell-$env command for that? Since conda-shell uses nix-shell itself, I was not able to just do the shell equivalent ... && conda activate $env.

Looking at and NixOS - Nixpkgs 21.05 manual I think I need to set the runScript attribute to something like bash -c "conda activate $env" in an overlay. Am I on the right track here?