Is there any way to highlight BETWEEN characters?

[dspwhite]

I can highlight individual characters using myScintillaBox.IndicatorFillRange(start, length);, but is there a way to highlight in between two characters - just with an approx 2 pixel width highlight? I'm creating an ultra sugary Regex wrapper program, and I'd love to highlight the zero-width matches it finds.

A related issue is to highlight carriage returns, again with a very narrow highlight.