The first question is, what do you mean by "Vancouver style"?
(Academics in England refer to something called "Harvard style," which
absolutely does not exist -- it turns out that each English university
has its own variant of author-date referencing, which somehow got the
label "Harvard" because supposedly the first person to propose it was
a Harvard scholar, somewhere around 1900; Harvard University Press,
however, does not publicly issue a style manual, and the most-used one
in the US is the Chicago Manual of Style.)
The answer is that it can only be done by someone with a grasp of XML
programming. The basics are available at
http://www.codeplex.com/bibliography
(hmm, it takes you to
http://bibword.codeplex.com/
)
by former contributor here Yves Dhondt, where you will find a
downloadable style called "Vancouver," but if the "Chicago" version
found there is indicative, you will find that it includes some
mistakes and some oversights that will need to be fixed up.
After years of asking for help here, I finally figured out how to make
the corrections myself and have a style that conforms to the _actual_
Chicago style in ways that the built-in Chicago style doesn't, and
also the one from Dhondt's site doesn't.