How to force CGI cache purge on POST?

[Ed W]

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 
request?

Thanks for any thoughts

Ed W