spit the data back as a base64 string and concat to build a data url to use as the .src of an iframe.
echo "data:" . $mimeType . ";" . $base64fileData ;
dataURLs are supposed to work in IE8, as long as the document isn't too big.
if you want 100% compatibility, you might just have to iframe the server response and give up on JS doing it for you.
BROWSER STATS [% share]
(2013/10/31) IE7:0.5, IE8:8.6, IE9:5.3, IE10:12.3, FF:17.7, CH:41.8, SF:8.1, MOBILE:20.4