I found soemthing that I think works, but it feels very hackish:

location ~ ^/([a-zA-Z0-9\-]+)/ {
error_page 418 = @apache; #proxy pass
recursive_error_pages on;
if ($arg_nc = 1) {
return 418;
}
try_files /cache/$1.html @apache;
}

Is this the best (only?) way to bypass a location based on query sting?