How to force CGI cache purge on POST?

Hi, I have a very simple website which could benefit from enabling cgi
caching. However, occasional updates are made to the site, exclusively
via a POST request.

For my simple purposes it would be sufficient to expire the entire cache
on any POST request (few hundred pages cached). How might I trigger
this to happen without modifying the backend CGI? ie is it possible to
make an nginx location which can trigger fastcgi_cache_purge on any POST

Thanks for any thoughts

Ed W