Recursive substitute-keyword-arguments / setting default on build system

[nils]

Hello,

I use a slightly customized emacs package, and want to use it as the package 
that is used in emacs-build-system for the emacs plugins I'm using.
The default emacs gets garbage collected and takes quite a while to reinstall, 
I would like to avoid that. Also, it seems cleaner to build the plugins with 
the exact version that they will be used with.

Here's what I have:

(define emacs-package
  ((const
     ((options->transformation
        '((with-configure-flag . 
"emacs=--program-transform-name='s/^ctags$/ctags.emacs/'")))
      emacs))))

(define (set-build-system-emacs plugin-package)
  (package
    (inherit plugin-package)
    (arguments
      (substitute-keyword-arguments (package-arguments plugin-package)
                                    ((#:emacs emacs) `,emacs-package)))))

(map set-build-system-emacs package-list)

>From what I can tell this does work for the packages in package-list, but not 
>for any inputs to those packages. That makes total sense to me, but I don't 
>know how to solve it.
Any pointers? Or is it possible to set the default package for a build system, 
removing the need for this mapping altogether?

Nils