Add --ignore-missing to git-pack-objects?

Hi.

Is it possible to add an option akin to git-rev-list's '--ignore-missing' to
git-pack-objects?

I use git bundles to (incrementally) backup my repositories. My script inspects
all bundles in the backup and passes their contained refs as excludes to
git-pack-objects to build the pack for the new bundle. This works fine as long
as none of these refs have been garbage-collected in the source repository.
Something like '--ignore-missing' would be really handy here to ask
git-pack-objects to simply ignore any of the passed revs that are not present
(anymore).

Thanks in advance.