Single-user Nix as root

TLDR: is it possible to execute single-user-nix-installed software as root?

Background: I have an ancient non-NixOS box which has got into some horrible inconsistent state. While trying to salvage it, I need to install some software and run it as root. The original OS’s package manager is failing me, so I’m trying to use nix to get around the problem. Multi-user Nix install fails. Single-user install works, but, as far as I am aware, this only works for non-root.