One thing I just noticed is this (which probably has been used before).
In article 153 that was referenced to earlier, there was explained a way (used in the Scriptorium under the file Faureve.nwc) that you could simply place the notes in the bottom staff with no ledger lines and then transpose them (but the staves had to line up exactly right). I've just discovered that, as in the example below, you can do the same thing without having to worry about where the staves are placed or how to transpose them. In the example below you will need two staves, the top one with a lower boundary of 12, and the bottom one with an upper boundary of 10.
Top Staff
!NoteWorthyComposerClip(2.0,Single)
|Clef|Type:Treble
|Key|Signature:Bb,Eb
|TimeSig|Signature:4/4
|Rest|Dur:4th|Visibility:Never
|Note|Dur:8th|Pos:-9z|Opts:Stem=Down,StemLength=0,Beam=First
|Note|Dur:8th|Pos:-7z|Opts:Stem=Down,StemLength=0,Beam=End
|Rest|Dur:4th|Visibility:Never
|Note|Dur:8th|Pos:-9z|Opts:Stem=Down,StemLength=0,Beam=First
|Note|Dur:8th|Pos:-6z|Opts:Stem=Down,StemLength=0,Beam=End
!NoteWorthyComposerClip-End
Bottom Staff
!NoteWorthyComposerClip(2.0,Single)
|Clef|Type:Bass
|Key|Signature:Bb,Eb
|TimeSig|Signature:4/4
|Note|Dur:8th,Slur|Pos:-4|Opts:Stem=Down,Slur=Upward,Beam=First
|Note|Dur:8th,Slur|Pos:0|Opts:Stem=Down,Slur=Upward,Beam
|Note|Dur:8th,Slur|Pos:13|Opts:Stem=Down,Beam,NoLegerLines,Muted
|Note|Dur:8th|Pos:15|Opts:Stem=Down,Beam=End,NoLegerLines,Muted
|Note|Dur:8th,Slur|Pos:-1|Opts:Stem=Down,Slur=Upward,Beam=First
|Note|Dur:8th,Slur|Pos:1|Opts:Stem=Down,Slur=Upward,Beam
|Note|Dur:8th,Slur|Pos:13|Opts:Stem=Down,Beam,NoLegerLines,Muted
|Note|Dur:8th|Pos:16|Opts:Stem=Down,Beam=End,NoLegerLines,Muted
!NoteWorthyComposerClip-End
The last two notes of each run (which are horrid to listen to) are muted, while the notes in the top staff are open headed notes with zero stem length. This takes care of the beaming, the slurring, and the extra midi notes that don't fit in the run. Now, I understand that this is not an absolute cure-all, because I'm sure there are many instances where this will not suffice, and it most likely has been used before, but I just thought I'd share it.