I would say that it is easier to do it with the limit blend (boundary blend) but perhaps also with the variable section sweep (in wildfire 5) selecting two trajectories with the ctrl and defining a section that however in the case represented by you must be a spline.
Bye.
Now I just miss to make a radius starting from 15 and comes to 2 as you see in the enclosed jpg... How do you recommend doing?https://drive.google.com/open?id=0b4a_sovruzphnlhwzhderwtlmmmnote the bastards having also put the ready prt to do so))))