You have to go the long hand way without cam, im thinking helical interpolation programmed in quadrants. Maybe use mastercam to draw a 3d spline of your tapered thread, break spline at qaudrant with line in 2d views and then use convert to arcs feature to obtain polar information to write program. It should read something like G3X10.Y10.Z-3.R10. And automatically should calculate the polar anchor point. Repeat this for however many quadrants, if one decimal place is wrong then all the code will fail.
Wisdom results from foolishness!