Forcing OMITTAG NO in HTML

I'm using Tidy to batch validate a website locally (via Selenium RC).
The pages are using the HTML 4.01 Transitional doctype in which end
tags are optional for many elements. However, for my purposes, a
missing end tag will usually signal a coding error in the HTML
template and I would like Tidy to warn about it despite the fact it's
valid HTML. Is there a way to do this other than writing a custom DTD
with OMITTAG set to NO? If not, how do I supply a custom DTD to Tidy
(running as a C library I think) and are there any disadvantages to
this approach?

Thanks,

  Tam.