Excluding packages by selecting different comps groups

[Joshua Aune <luken@xxxxxxxxx>]

Is there a way to exclude a package when a comps group is selected?  If
at all possible I would like not have to modify anaconda to do this,
just the comps file.

For example, in the following comps file PkgA2 conflicts with PkgB2.  I 
want PkgA2 installed instead of PkgB2 if 'Group A' is selected (during a
custom install).  Is there a way to put a priority on a package?

0 Group A {
  PkgA1
  PkgA2
}

1 Group B {
  PkgB1
  PkgB2
}

I have tried the following, but pkgorder (and I would assume others) 
don't like this syntax.
1 GroupB {
  PkgB1
  ? ! Group A {
    PkgB2
  }
}

Is there a group or similar keyword so something like this would work?
(group !Group A): PkgB2

Thanks,
Joshua Aune