help with distributed workflow/signoff

Hi, I'm new to the list and have a question about signoffs, and the details of how distributed workflows work in the wild.

We are looking at converting a large group of developers from using svn to git.
 Our current svn workflow relies on external tools and commit hooks to present
(poorly) a somewhat distributed model that would be natural with git. 
Unfortunately, we have not been able to connect a few of the dots that we need
for our git based workflow.  We have a basic idea, loosely based on workflows
presented in online sources and the "Pro Git" book:

  Developer -> GateKeeper -> Master Repository

Developers wishing to contribute code would push revisions to the gatekeepers' repos, who after reviewing the revisions would push them to the Master repository, from which developers would have only pull access. The GateKeeper repositories would be well known, and observers could easily see which GateKeepers had which revisions in their review queues.

This works fine, except for the fact that there is no trail in the master repository indicating which GateKeeper approved which revision.

We've scoured the internet for solutions. One idea we have tried and abandoned is using 'git commit -s --amend'. This does create a new revision with the signoff information we want, but the problem is that it creates a new revision. Eventually, the developers (and the GateKeeper repository) will end up with both the revision containing the signoff and one without it.

I've seen evidence of what we're after - by browsing the repository of git itself. Each revision in it contains an "Author" field and a (frequently different) "Committer" field. Furthermore, there are often multiple "Signed-off-by" and "Acked by" logs. How are these fields populated? Are new revisions created each time the sign-off information is added? If so, how do the contributors deal with these new revisions when synchronizing with the master later? How are the pre-signoff revisions purged from the bare GateKeeper repositories?

I would greatly welcome and advice on how these workflows are implemented.

Thanks in advance, Brock Peabody