How to revert one of multiple merges

Branch A, B, C each have 20 commits, 0-19.

Branch v1.0.0 created, then merge of A, B, C performed.

After testing, we realize that the branch B is not ready for production release and we'd like to remove it from branch v1.0.0.

If I do

% git merge A B C

I get a single commit:

% git log -p

commit 1644a0b98c01869aa83e59aa41374c22098c47b6
[...]
Date:   Fri Oct 16 09:52:32 2009 -0500

    Merge branches 'A', 'B' and 'C' into v1.0.0

[20 x 3 commits]

If I do

% git merge A % git merge B % git merge C

Then:

% git log -p

commit 8946edd381384d0882221c87b5b3b7bf47127d70
[...]
Date:   Sat Oct 17 21:28:36 2009 -0500

    Merge branch 'B' into v1.0.0

commit 076ed422443e3684e564f7cae2b92e4538088ae6
[...]
Date:   Sat Oct 17 21:28:35 2009 -0500

    Merge branch 'A' into v1.0.0

but no "Merge branch 'C' into v1.0.0".

And so, I'm faced with git rebase -i posing some unanswerable questions to our release manager. She cannot easily remove B from the merge after doint either merge A B C, or merge A, merge B, merge C.

Can anyone help?

Bill