one half of a rebase

[Geoffrey Irving <irving@naml.us>]

If I'm on branch topic and do "git rebase master", git performs two operations:

1. Rewind the current head to master.
2. For each commit in topic that isn't in master, cherry pick it onto
the current head.

I would like to be able to do (2) as a separate operation.  For
example, if I start out on branch master and want to get all of
topic's commits on top of the current head, I currently do

    git checkout topic
    git rebase master
    git branch -d master
    git branch -m master

If I could do (2) as a separate operation, it would look something like

    git cherry-pick-all topic

which is simpler and faster since it avoids switching files back and
forth (master to topic and back).  Is there a robust way to achieve
the cherry-pick-all semantics with current commands?  If not, how
difficult would it be to partition rebase accordingly?

Thanks,
Geoffrey