You can add a Marker in front of the second and later triplets in your score, with the marker's Triplet box checked, and its visibility set to Never. This hides the triplet marking. See the following clip for an example.
!NoteWorthyComposerClip(2.75,Single)
!NoteWorthyComposerClip(2.75,Single)
|Clef|Type:Treble
|Note|Dur:8th,Triplet=First|Pos:-1|Opts:Stem=Up,Beam=First
|Note|Dur:8th,Triplet|Pos:-1|Opts:Stem=Up,Beam
|Note|Dur:8th,Triplet|Pos:-1|Opts:Stem=Up,Beam
|Note|Dur:8th,Triplet|Pos:-1|Opts:Stem=Up,Beam
|Note|Dur:8th,Triplet|Pos:-1|Opts:Stem=Up,Beam
|Note|Dur:8th,Triplet=End|Pos:-1|Opts:Stem=Up,Beam=End
|Marker|Pos:0|Target:Triplet|Visibility:Never
|PerformanceStyle|Style:Simile|Pos:-6.5
|Note|Dur:8th,Triplet=First|Pos:-1|Opts:Stem=Up,Beam=First
|Note|Dur:8th,Triplet|Pos:-1|Opts:Stem=Up,Beam
|Note|Dur:8th,Triplet|Pos:-1|Opts:Stem=Up,Beam
|Note|Dur:8th,Triplet|Pos:-1|Opts:Stem=Up,Beam
|Note|Dur:8th,Triplet|Pos:-1|Opts:Stem=Up,Beam
|Note|Dur:8th,Triplet=End|Pos:-1|Opts:Stem=Up,Beam=End
!NoteWorthyComposerClip-End