Adding new persistent relative time ranges

I often want a Relative Time range that is not on the default list. For instance, I use now-10d a lot. Although recent Absolute Time ranges are saved for re-use there does not appear to be a similar option for Relative Time ranges. In the Dashboard Settings you can create/edit the Auto-Refresh periods. Can we have a similar for the relative time list?

I am a fairly new user (3 months) so I apologize in advance if this is already available.