How to move mesh vertices without making a copy

Hi,
I have a mesh with over 100 000 vertices. In my plugin I turn on grips and select an area of vertices that I want to move. Then I do a GripUpdate to update the model. This takes a very long time to do this update.
If I do the same operation directly in Rhino I can click and drag and the vertices and they follow smoothly in real time.
My question is, is there a way to do this from Rhinocommon?
I believe it is the copy and replacing the mesh that takes time. Som what I want to do is just changing the position of the vertices and then update my view.

Thanks,
Arne