Output cache - caches even with POST?

[eluser]markowe[/eluser]
As you probably know, CI's output cache function does a nice job of caching output into flat files on a per controller basis. As I understand it, the file name generated is an md5 of the uri string and the function looks for this on each page load, expiring it if necessary, or serving up the flat file if not, and a huge speed difference there is too.

But it does not take account of a form submission, i.e. user POST. For example, I have a page of product listings and the user can further filter the results by selecting form options (by date, by city, whatever), which are also optionally saved to a session cookie.

The output cache fuunction apparently does not take account of this and will serve up the same cached page regardless. What is the simple way round this?