Adding the code above to line 822 of swivelButton.rb fixes the preview image:

Sketchup.active_model.active_view.zoom_extents

Then modify line 572 of swivelButton.rb from:

  standoff_distance = getStandoffDistance() * 1.1;

to

  standoff_distance = targetNow.distance eyeNow

Add the following line above line 583 so you end up with:

  standoff_eyepoint = eyeNow;
  centerpoint.z = standoff_eyepoint.z;

Comment out lines 656 to 663:

# 	bb=Sketchup.active_model.bounds
# pmax = bb.max
#	pmin = bb.min
#	zdiff = bb.max[2]-bb.min[2]
#	pcenter = bb.center
#	targetNow = pcenter
#	up = Geom;;Vector3d.new(0.0,0.0,1.3*zdiff)
#	upTarget = pcenter + up

The code before tried to fit the entire model into the view by getting the bounding box of the active model and drawing a circle around it, then panning the camera around that circle.

My fix, simply draws a circle around the model from the current cameras position and then pans around that circle.