Unfortunately, so far(0.8.7), not to solve this problem :(
I read the source code, ngx_http_static_module.c documents found this piece of code inside
    if (r->method & NGX_HTTP_POST) {
        return NGX_HTTP_NOT_ALLOWED;
    }
Posted at Nginx Forum: http://forum.nginx.org/read.php?2,2414,4549#msg-4549