Thanks for the prompt answer - even if it wasn't exactly the answer I wanted.
Just to get creative here:
Would it be possible to create a custom image that would be small enough to fit in /update so I can actually _ota it, and in that image include a new partition table? So I'd essentially load 2 images. The first image would be just to upload a new partition scheme, the second being the actual image?
That wouldn't be possible. Although, you could built a new image and increase the partition size, however you would have to flash the new image through the Flash Tool Lite (or the flashall method). The following document might be of your interest: Increasing the Root Partition Size.