With a sample from Balaji Ramamoorthy I was able get it working for now.
That's the example he gave you?
To merely rotate the grip, you can just push/pop the model transform
before/after supermessaging the base class's ViewportDraw method, and
there's no need to draw it yourself.
See Geometry.PushOrientation() and Geometry.PopOrientation() in the docs.
The first would be called before you call base.ViewportDraw(), and the
second would be called after it returns.
If this is a representative example of the kind of support that paying customers get, then they're getting robbed.