So I "reached out" to Nikolai Faaland (he runs the Virtual Earth 3D team blog) and he figured this out. I told him what I was trying to accomplish and sent him the code I was working with. He figured out that the answer is in the "DoMapPivot"
method. He said to make a copy of this method and call it "DoMapPivotUpDown". Then all that is needed is to change a few lines of code in order for it to work.
Comment (or remove) the following lines:
//Vector3D tempVector = anchor.Vector;
//anchor.Altitude += 10;
//Vector3D axis = Vector3D.Normalize(anchor.Vector - tempVector);
Add the following line of code (it replaces the previous variable called "axis"):
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axis = Vector3D.Cross(cameraStep.Camera.Viewpoint.Orientation.LookUp, cameraStep.Camera.Viewpoint.Orientation.LookAt);
That's it! I now have a method that allows me to "tilt" while maintaining focus on the center of the screen (similar to holding down Ctrl key while mouse dragging in Bing Maps 3D). I wired this up to a gesture (palm of the hand + finger drag) and
it works like a champ!