57
If you aren't concerned about playback, you can make a small code change in the plugin to allow two user objects to precede a split chord. Go to line 98:
if (idx:userType() == userObjTypeName) then return false end
Add "--" to the start of the line to comment it out (or, if you are brave, you can delete it)
It will now display and play a tremolo for both sides of the chord, but as previously noted, the longer duration note will play too short.
I haven't thoroughly tested this change to know if there are any side effects, but I suspect that it will work fine.
EDIT: You can disregard this hack, I went ahead and made an update.
89
Glissando.ms is what you want to use. You will need to add two of them, and offset one of them for the upper note pair. I attach an example score.
!NoteWorthyComposerClip(2.751,Single)
|Chord|Dur:Half|Pos:1|Opts:Stem=Up|Dur2:Half|Pos2:-3
|User|Glissando.ms|Pos:3|Class:Span|StartOffsetY:4.3|EndOffsetY:2.1|Pen:wavy|Text:
|User|Glissando.ms|Pos:3|Class:Span|Pen:wavy|Text:
|Bar
|Chord|Dur:8th|Pos:2,#4|Opts:Stem=Up,Beam=First
|Chord|Dur:8th|Pos:#1,#3|Opts:Stem=Up,Beam=End
!NoteWorthyComposerClip-End