How to see /etc/nixos in an custom fhs

Hi, just switched to 21.05 and saw the new vscode-fhs

tried it, however I cannot see nor edit /etc/nixos any longer in there… that is a pity, because I edit it quite often and would like to use vscode for editing.

Is there a way to make /etc/nixos visible within a custom fhs? Why is it gone?

Because it is not bound:

thank you very much for the pointer to the source code. It looks hard-coded…

Is there a generic default bind to the old system (including /etc/nixos for me), or is this 100% hidden now in an buildFHSUserEnv?