./pre-inst-env with extra channels

[EuAndreh]

How can I use the Guix version of my Git clone, alongside its packages, 
services, etc. while still using extra channels?

Sample run: a build of my current system works:

    $ guix system build /etc/guix/configuration.scm
    /gnu/store/gfn6hpim1njlnr0d3p6mmvc4zgqmgqw6-system

But when trying to use the code from my clone, it fails to recognize the 
extra channels, available in the system-wide /etc/guix/channels.scm file:

    $ ./pre-inst-env guix system build /etc/guix/configuration.scm
    guix system: error: failed to load '/etc/guix/configuration.scm':
    ice-9/boot-9.scm:3330:6: In procedure resolve-interface:
    no code for module (xyz euandreh queue)