Impossible. You can import stl as facet body, you can use it as "background" to create some scketches for 3d modeling. You can try to "best fit" your scan data with cylindef or another simple primitive. Some time ago I build ugopen applicarapplication for convert stl-》solid body, non parametric.
The old Imageware tools could do this.
They're embedded in NX somewhere - and I'm not sure how they're licensed.
Production: NX10.0.3.5 MP16/TC11.2
I'd rather be e-steamed than e-diseaseled
I think we don't have a direct converter in NX, because sometimes you have to manually sketch it over again. but you can just specify some points and create a surface using NX rapid surfacing. Just import your STL file to NX then go to Menu-->Insert-->surface-->Rapid Surfacing, or just use the command finder.
use this video as a guide.
starting with NX8.5 you can use the "fit surface" command for reverse engineering. The command gives you the option to rebuild associative surfaces based on scaned data as freeform surfaces, planes, spheres or cylinder or cones.
But you need the studio surface license.
We use this feature for reverse engineering of forging dies with a lot of freeform surface with very good results.
Production: NX10.0.3, TC 10.1.4