Ok I also tried this:
if (-e /wp-content/cache/supercache/$http_host/$request_filename) {
rewrite ^(.*) /wp-content/cache/supercache/$http_host/$1index.html
break;
}
Check and see if this directory is here based on the requested file
name. If it's there use this rewrite rule.
Didn't work either. Anyone else got any ideas?