I have not used this yet with my students, but the Florida Center for Reading Research has some fluency activities that chunk parts of the sentences together in meaningful phrases. I would think, as the previous posters mentioned, that if they are chunking correctly in their spoken language, perhaps they would be more likely to chunk in their written work.
http://www.fcrr.org/Curriculum/PDF/G...3Fluency_3.pdf
I don't know if this would help address your issue, but it might. If you use it, let us know if it works!