Installing new fonts for groff typesetting

In other distributions, I add additional fonts to groff by copying converted font files into the directories:

/usr/share/groff/current/font/devps

and

/usr/share/groff/current/font/devpdf

I also have to modify the “download” files in each directory to reflect the additional fonts.

If anyone would be willing/able to help, I would really like to know how I can do the aforementioned operations in NixOS.
Thank you.