Hi Simon, are you still interested in solving this? Sorry, it has taken me forever to get through some of the backlog here. If you are still interested, I can brainstorm on this with you, though I'm not sure we'll arrive at a perfect solution. The adapted versions of the controls aren't complete mimics of the unadapted versions. Some features and attributes are not supported in the adapted versions. Showing lines in the tree view is one such currently unsupported feature.
Still, I wonder if you could basically accomplish your goal in other ways that the adapters do support. For example, though it wouldn't be an exact mimic, you might be able to use CSS borders to accomplish some visual notion of lines between parts of the tree. Have you explored that idea yet? As I said, though, I don't think there is any simple solution (that I know of) to mimic exactly the unadapted lines that can be shown when you are using the adapted tree view.
Russ Helfand
Groovybits.com