Otherwise I need to use yum, instead of my preferred zif backend.
To do this for pkcon we would need new DBus API which we've already half-discussed on the mailing list. When we've come to some kind of decision on how to implement it, it'll be easy to add the zif parts. Other distros actually have the build-depends for the source package much easier (e.g. gentoo) but others like apt it's much harder.
In the meantime, I've added a new subcommand to zif:
Author: Richard Hughes <email@example.com>
Date: Sun Sep 18 14:56:07 2011 +0100
Add a new command 'build-depends' to install packages needed to build other packages
:100644 100644 9920f5a... bf008a9... M tools/zif-main.c
I think punting this to the zif command line is okay for the moment, as programmers using the command line will want package build-depends, and we don't actually need it in any GUI or interactive programs just yet.
If you could checkout zif from git master and give it a try I'd be most grateful. Thanks.