Bob Royce (notable US mirror maker) has a design with a rotating UTA here:
http://www.rfroyce.com/newtonian8f8.htm
I copied Paul's approach for rotating UTAs for my bino. But in this case the UTAs only rotate a few degrees, just to adjust interpupillary distance. Geoff's point about the challenge of maintaining collimation for tubes moving through larger arcs is well taken.