To have fingering for NWC files with piano, you can easily just type in text. For example if you want a D# to be played with your right index finger, just click x (text expression), then type a 2 under the note. Make sure it can be seen. You can insert multipe fingering numbers by selecting "at next note/bar" instead of "best fit" in expression placement.
Another way to do this (if there are no lyrics) would be to type the fingering in the lyrics portion. That way the fingering would automaticaly show up under the desired notes.