AER73,
In answer to your direct question I do not know how to make the dimension display as you want. However, you might try just using a note.
ArtL, you are correct that if you can't measure it you shouldn't dimension to it. However, I'll bet that this feature is only incomplete in this section and that its diameter is complete in a perpendicular view. AER73, you might consider showing the perpendicular view so the dimension would show without confusion.
- - -Updraft