Try this. I wrote it for machine screws but it should work for your NPT, just incorporate the thread taper into the sweep profile.
1) Create a shaft at the major diameter of the thread<?:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" />
2) InsertHelical Sweep Cut
a) Constant Pitch, Thru Axis, Right or Left Handed
b) Sketch Sweep Profile