[RFH] specifying rebase options when branch.<name>.rebase = true

In setting up our rebase-based workflow I'd like people
to simply use "git pull".  But "branch.<name>.rebase=true"
gets me only halfway there.

The problem is that I'd like to rebase local merges as well,
but have not seen a was to specify the --preserve-merges flag.

Am I missing something obvious?