The book LIVING LANGUAGES edited by Nancy Buffington et al.contains
an essay entitled "The Invisible Discourse of the Law."  A good
way to introduce grammar to lawyers, I would think, would be to have
them read such essays which show how sneaky and bad lawyerly
language is. And to study the grammar of bad legal language.
 
Another thought: Look at the redundancies in language ( a noun occupies
a position, it has determiners in front of it, it has noun suffixes,
it has plural inflections, etc.), and compare those redundancies with
legal talk (assault and battery, etc.)
        --Bill Murdick