After some more private discussion (I forgot to CC the mailing list) 
with Jon Nelson,
he came up with this strategy for fixing the author/email part of commit 
messages:

0. Make a backup copy of the repository, just in case.

1. Setup your GIT_AUTHOR_xxx/GIT_COMMITTER_xxx env. variables correctly.

2. Apply the attached patch to recent git sources. (patch made by Jon 
Nelson).

3. Run the patched git-convert-objects, passing HEAD as argument.

4. Run "git-update-ref HEAD 'newsha1'", where 'newsha1' is the output 
from the previous command.

5. Run "git-prune" to get rid of the old stale object files.

This worked for me, but I guess there are no warranties 8)
In case you have multiple branches you might need to repeat the 
procedure for each branch.

thanks Jon

//Jacob