Please disregard, I just found the solution I was looking for in the documentation:
http://boost-sandbox.sourceforge.net/libs/xpressive/doc/html/boost_xpressive/user_s_guide/examples.html#boost_xpressive.user_s_guide.examples.find_all_the_sub_strings_that_match_a_regex_and_step_through_them_one_at_a_time

I apologize for my premature post.