add-apt-repository and snapcraft cleanbuild?

[Dan Kegel]

Hey all,
Day 3 of using snapcraft, and I've managed to get
both piglit and a proprietary app snapped and running.
Snapcraft's learning curve is not too steep, kudos.

Problem: I can't do 'snapcraft cleanbuild' on my proprietary
apps because they depend on packages in a ppa and/or a
private apt repo.
Is there a way to specify add-apt-repository foo
to be used during snapcraft cleanbuild?