The rotation point is inherited from the 3D model ‘origin’ point. It is therefore possible to change that in 3D modelling software and re-save the mesh with a modified rotation point. There is no option for manipulating the rotation point directly in Isadora.
The other option is to use the 3D Stage Orientation actor. It provides another layer of 3D movement, this time as a viewport/virtual camera. Therefore you can use a combination of rotation settings to create movement in different arcs.