Symlinks in fhsuserenv

I’ve downloaded a program that expects sbcl installed at /usr/local/lib/sbcl, but an fhsuserenv made with sbcl in it has sbcl installed at /usr/lib/sbcl, so this program doesn’t work, and I can’t make symlinks in an fhsuserenv (readonly filesystem).

How do I modify the structure of an fhsuserenv? Does it have an argument that can be used like this:

pkgs.fhsUserEnv {
  symlinks = {
    "/usr/local/lib/sbcl" = "/usr/lib/sbcl";