Pickaxe usage question -- only matching on added string

Documentation for diffcore-pickaxe (in Documentation/diffcore.txt) says:

When diffcore-pickaxe is in use, it checks if there are
filepairs whose "original" side has the specified string and
whose "result" side does not.  Such a filepair represents "the
string appeared in this changeset".  It also checks for the
opposite case that loses the specified string.

Now, is there a way to get diffcore to match only on 'added' (or on
'removed', for that matter)? I am tring to identify commtis that added
patches to a project, and I seem to be getting matches that add and
remove when I do:

   git-whatchanged -p -C -S"\t" master

cheers,


martin