Exclude repositories during backup

I’m wondering if there is a way to exclude select repositories from a backup event. I currently have an Omnibus configuration and invoke a backup using the command:

sudo gitlab-rake gitlab:backup:create source

My current Git instance holds several repositories that I would like to have backed up; however, there are a subset of repositories that I do not wish to backup. These primarily include third-party repositories such as the Linux Kernel and more.

As a current workaround, I’m currently thinking of hosting two instances of GitLab; one with important projects which performs a backup more aggressively and an alternative/third-party instance which is much more relaxed (or even non-existent). I’d rather not use this approach to prevent maintaining another Git instance.

Any help is appreciated.