Have a variable to point to installed library paths

Related to https://github.com/ocaml/dune/issues/1185 but a bit simpler.

In a few places I would like to get the place of where the current library (or one of the already present libraries) is installed. To do this I have come up with this very inelegant solution, which seems to work fine:

(rule
  (target install-dir)
  (action (with-stdout-to install-dir
    (bash "echo $(dirname %{lib:<lib>:META})"))))

And now other rules could just (:include install-dir) when they want to refer to the path where <lib> is installed.

Is there any way to make it simpler? E.g. by expanding %{lib:<lib>} to the parent directory of %{lib:<lib>:META} or %{lib:<lib>:dune-package} ?