Removing a commit from a local branch

Hi List,

I'm part of a development team using git. We use a maintainer model
where developers send patches/pull requests to a maintainer who
applies the patches to a local branch, decides if they're good or not
and pushes the good patches to the public repository.

What I want to do is script the removal of a bad patch so that the
maintainer identifies a patch in his local branch, sends an email to
the author telling them why their patch is being rejected then removes
the commit for that patch. Using git log a script can extract the
author email address, hash and headline of each commit. Based on that
information scripting the email is easy enough. Now I come to using
git rebase to remove the bad commit based on its hash which leads me
to my question - How do I refer to a commit based on the hash of its
parent?

Consider the following example. The maintainer has the following branch locally

  todeliver: A-B-C-D

He is happy with commits A, C and D but wants to reject B. Ideally I
want to be able to say
  git rebase --onto <parent of B> <child of B> todelvier

and get
  todeliver: A-C'-D'

I know that <parent of B> can be referred to as B~1 but what about
<child of B>? I've read through the man page for git-rev-parse and
nothing stands out as child of commit X.

Is there a better what do achieve what I'm after?

Thanks,
Chris