Lawrie created several fonts (the Purdy fonts) for use with NWC. He included symbols for courtesy accidentals that include the sharp, flat or natural signs. You enter the courtesy accidental as text where you want them. Vertical placement might be tricky, but you can get close enough in most cases. One drawback is that if you transpose the staff, the text needs to be moved manually, and if you have lots of these text entries, it's tedious.
This is a way to put courtesy accidentals above or below the note and uses the font NWC already has installed, using Rick's example:
!NoteWorthyComposerClip(2.5,Single)
|Clef|Type:Treble
|Key|Signature:Bb,Eb,Ab|Tonic:C
|Note|Dur:32nd|Pos:1|Opts:Stem=Down,Beam=First
|Note|Dur:32nd|Pos:2|Opts:Stem=Down,Beam
|Note|Dur:32nd|Pos:1|Opts:Stem=Down,Beam=End
|Bar
|Note|Dur:Half|Pos:n0
|Rest|Dur:4th
|Bar
|Note|Dur:8th|Pos:n3|Opts:Stem=Down,Beam=First
|Note|Dur:8th|Pos:5|Opts:Stem=Down,Beam=End
|Note|Dur:8th|Pos:5|Opts:Stem=Down,Beam=First
|Note|Dur:8th|Pos:3|Opts:Stem=Down,Beam=End
|Text|Text:"f"|Font:StaffSymbols|Pos:6|Placement:AtNextNote
|Note|Dur:16th|Pos:0|Opts:Stem=Down,Beam=First
|Note|Dur:16th|Pos:5|Opts:Stem=Down,Beam
|Note|Dur:16th|Pos:3|Opts:Stem=Down,Beam
|Note|Dur:16th|Pos:0|Opts:Stem=Down,Beam=End
!NoteWorthyComposerClip-End