You can solve this via the XNA API by setting a model matrix for the skeleton. Please search the web for "XNA rotate around pivot" for examples.
If you want to solve this using Spine, you have to introduce a bone parented to the root bone, to which all other things are parented. Here's an example using Spineboy.
The root bone has a child bone called pivot-child. The rest of the skeleton is parented to pivot-child.
The root bone thus becomes the pivot. You can adjust the x/y position of the pivot-child, which is relative to the root bone. Then you can rotate the root bone.
