Well as it turns out, it was already a mime type, I just needed to name my static files as .json! Im guessing .json is pretty standard.
My main reason for doing this, is so that multiple channel viewers will not put a strain on the database. Also if the database every goes down, the static file is set.
For anyone using PHP, it's a piece of cake
$json_data = json_encode($JSON2);
All I did was replace
echo json_encode($JSON2);
with
file_put_contents('.../output.json, $json_data);
note: the 'user' on your server that your webserver / php shows up as will need permission to write to the directory on which you place this.