Pre-processing the request body

Hi folks,

I have a mod-perl app on the receiving end of a POST from a credit card
company, and they are sending the data as application/x-www-form-urlencoded
but they aren't URL-encoding UTF-8 characters.  When I give that malformed
data to Apache2::Request it refuses to see any POST variables atall.

This company generally don't understand charset/header issues, so instead of
going through some pain, I'd like to re-write the request body and the
Content-Length header.

What is the most modperl-like way to do that?

I'm guessing the sort of filter described here
http://perl.apache.org/docs/2.0/user/handlers/filters.html#All_in_One_Filtermight
be best, but has anyone made a wrapper that allows, for example, regex
search+replace on the request body and header-rewriting?

thanks
John