I don't know if there's s a simple way to do it, i just checked out the CandCNC website out of curiousity and couldn't find the plug in.
Anyway, what do you use for CAD/CAM? What I use is Rhino and RhinoCAM and what I do is draw the part and the thing it's going to go to and then slice the tube from the other part to create a tube miter, then I use Curve>Duplicate Edge and that gives me a line that is the shape of the miter, then I use the 4th Axis engrave option to follow that line.
NOW I've never actually cut a tube miter this way YET, but will be later this week and this seems as though it might work.