From the docs, there doesn't appear to be a way to resize disks at all.
One of the utilities I want to build is the ability for a machine to automatically grow its disk in response to a low diskspace event (which, of course, has caveats, so I'll be building checks and approvals in), but essentially, the disk update spec should accept a new capacity for the backing spec (REST API - update ). So, if anyone else out there has need, please comment (or let me know if you are aware of a way to do this!)
Thanks!
--Matt