Assuming an initial Tempo of Q=80 and a reasonable Staff Italic font size, this would seem to satisfy the intent, both musically and visually. This, of course, will complicate the other staves.
!NoteWorthyComposerClip(2.0,Single)
|Bar
|Tempo|Base:Quarter Dotted|Tempo:80|Pos:6|Visibility:Never
|TimeSig|Signature:12/8|Visibility:Never
|Rest|Dur:4th,Slur
|Text|Text:"3"|Font:StaffItalic|Pos:10|Justify:Center|Placement:AtNextNote
|Note|Dur:4th,Slur|Pos:-4
|Note|Dur:4th,Grace|Pos:-3^|Visibility:Never
|Note|Dur:4th,Grace|Pos:3^|Opts:Stem=Down,Muted|Visibility:Never
|Chord|Dur:4th|Pos:-3,3z|Opts:Stem=Up,StemLength=1
|Note|Dur:4th,Slur|Pos:3
|Note|Dur:4th,Grace|Pos:b3^|Visibility:Never
|Note|Dur:4th,Slur|Pos:b3
|Text|Text:"3"|Font:StaffItalic|Pos:12|Justify:Right
|Note|Dur:8th,Triplet=First,Slur|Pos:2|Opts:Stem=Down,Beam=First
|Note|Dur:8th,Triplet,Slur|Pos:b2|Opts:Stem=Down,Beam
|Note|Dur:8th,Triplet=End|Pos:1|Opts:Stem=Down,Beam=End
|Bar
|Tempo|Tempo:80|Text:"T°"|Pos:6|Visibility:Never
|TimeSig|Signature:Common|Visibility:Never
|Note|Dur:Half|Pos:n0
!NoteWorthyComposerClip-End
BTW, how are you interpreting the 2nd measure of 2Ellingtons_nested_triplet.jpg ?
It seems to have too many beats.