I haven’t looked into the ViewportControl, but from it you can get the RhinoViewport, which you can manipulate via code.
I’d go with the Eto sample app. There the ViewportControl is derived from Eto.Forms.Control, which has all the regular input events as one would expect from a control.
So you’ll have to handle that yourself, and drive the underlying RhinoViewport yourself via code.
Note that I haven’t tried this myself, this is all just an educated guess.