Something I've tried on my 10" newt was the Wilcox solution:
http://www.andysshotglass.com/wilcox...ing_rings.html
I got some large stainless steel hose clamps and some clear plastic tubing. I had to join 2 hose clamps together to get a large enough diameter to fit around the scope. You slide the hose clamp through the tubing then wrap it around the scope and re-connect the ends of the hose clamp. I got all the parts from Bunnings.
http://www.bunnings.com.au/kinetic-1...lamps_p4920201
Parallax make rotating rings however these cost quite a lot and are very heavy.
http://www.parallaxinstruments.com/rings.html