Originally posted by Jim311
The mechanic said that they don't make cable stops for that large a diameter of tubing 
Sure they do! Jamis even has a part# for an adapter, but I just used a universal one on mine. Maybe a well trained Cannondale shop can look one up for your brand.
I measured the ID of the tubing hanger at .24" or 6.1mm, and would think it is just industry standard. If the flange on the cable end is large enough to keep it from going through, that is really all you need.