Setting custom encoding for a single request?

Hi all,

I was wondering if it's possible to set Rails's output encoding for a
single request w/ Ruby 1.9?

For example, one request on my app generates a form for submission to a
third-party who mandates ISO-8859-1, and the form therefore contains
iso-8859-1 encoded strings.

Although I set the response's content-type to 'text/html;
charset=ISO-8859-1', when Rails renders the output it produces a UTF-8
string (containing ISO-8859-1 characters) and then falls over with an
"ArgumentError (invalid byte sequence in UTF-8)".

Is is possible to tell Rails "generate all output for this request in
charset x?'