Your best bet for this type of notation would be to insert a rest symbol as a text object, per the following example:
!NoteWorthyComposerClip(2.751,Single)
|Text|Text:""|Font:StaffSymbols|Pos:7.5|Justify:Center|Placement:AtNextNote
|Chord|Dur:8th,Triplet=First|Pos:-1,1,3|Opts:Stem=Down,Beam=First
|Chord|Dur:8th,Triplet|Pos:-1,1,3|Opts:Stem=Down,Beam
|Chord|Dur:8th,Triplet=End|Pos:-1,1,3|Opts:Stem=Down,Beam=End
!NoteWorthyComposerClip-End
NWC does have the ability to combine a rest with a chord, but the rest duration cannot be greater than the duration of the chord to which it is attached.
It is, but at some point you are going to need to control the Stem Length of the notes. If you use a split chord, you get the same Stem Length for each voice. I would suggest something like this:
!NoteWorthyComposer(2.751)
|AddStaff|Name:"Staff"
|StaffProperties|EndingBar:Open (hidden)|WithNextStaff:Layer
|Marker|Pos:-7|Target:Triplet|Visibility:Never
|Rest|Dur:8th,Triplet=First|Visibility:Never
|RestChord|Dur:4th,Triplet=End,Slur|Opts:Stem=Down,Slur=Upward,XNoteSpace=0.5,NoLegerLines,Muted,HideRest|Dur2:Whole|Pos2:7z
|Marker|Pos:9.5
|Note|Dur:4th,Slur|Pos:5|Opts:Stem=Up,StemLength=5.5
|Rest|Dur:4th,Slur|Opts:VertOffset=8
|Marker|Pos:9.5
|Note|Dur:4th,Slur|Pos:6|Opts:Stem=Up,StemLength=5.5
|Bar
|AddStaff|Name:"Staff-2"
|StaffProperties|EndingBar:Open (hidden)
|Marker|Pos:6|Target:Triplet
|Rest|Dur:8th,Triplet=First
|Chord|Dur:8th,Triplet|Pos:-2,1,3|Opts:Stem=Down,StemLength=5,Beam=First
|Marker|Pos:7|Target:Triplet
|Chord|Dur:8th,Triplet=End|Pos:-2,1,3|Opts:Stem=Down,StemLength=5,Beam=End
|Marker|Pos:6|Target:Triplet|Visibility:Never
|Chord|Dur:8th,Triplet=First|Pos:-2,1,3|Opts:Stem=Down,StemLength=5,Beam=First
|Chord|Dur:8th,Triplet|Pos:-2,1,3|Opts:Stem=Down,StemLength=5,Beam
|Chord|Dur:8th,Triplet=End|Pos:-2,1,3|Opts:Stem=Down,StemLength=5,Beam=End
|Marker|Pos:6|Target:Triplet|Visibility:Never
|Chord|Dur:8th,Triplet=First|Pos:-1,1,3|Opts:Stem=Down,StemLength=6,Beam=First
|Chord|Dur:8th,Triplet|Pos:-1,1,3|Opts:Stem=Down,StemLength=6,Beam
|Chord|Dur:8th,Triplet=End|Pos:-1,1,3|Opts:Stem=Down,StemLength=6,Beam=End
|Marker|Pos:6|Target:Triplet|Visibility:Never
|Chord|Dur:8th,Triplet=First|Pos:-1,1,3|Opts:Stem=Down,StemLength=6,Beam=First
|Chord|Dur:8th,Triplet|Pos:-1,1,3|Opts:Stem=Down,StemLength=6,Beam
|Chord|Dur:8th,Triplet=End|Pos:-1,1,3|Opts:Stem=Down,StemLength=6,Beam=End
|Bar
!NoteWorthyComposer-End