How do you make a special ending that covers two or more measures rather than just one?
A special ending is terminated by the master repeat end mark. So the special ending will reach from where you mark it to the master repeat end or if there is no master repeat end, to the end of the music (or DS instruction etc).
If you want the bars included within the particular special ending to be marked with a line, you can add a continuation by clicking on the "continue prior ending" button within the special ending menu,
Like this:
!NoteWorthyComposer(2.751)
|AddStaff|Name:"Staff"
|StaffProperties|EndingBar:Open (hidden)
|TimeSig|Signature:2/4
|Note|Dur:Half|Pos:-1
|Bar
|Ending|Endings:1
|Note|Dur:Half|Pos:0
|Bar
|Ending
|Note|Dur:Half|Pos:0
|Bar|Style:MasterRepeatClose
|Note|Dur:Half|Pos:1
|Bar|Style:SectionClose
!NoteWorthyComposer-End