You have don't posted some image so it's difficult to say something ;)

I have made that in the past, I suppose it's easy to adapt for nurbs ;)
A quarter of sphere on a plan 3D trimed add thickness if necessary

Just what I needed.

Thanks!

I don't know if it is a good way, but its fun(shows off MOIs wonderful snapping features) and 'green' - with a mileage of two curves per model/gallon :)

All roads go to Rome ;)