Have a look at this post:
Bascially you can store the following bookmarklet (what is a bookmarklet) in your favourites toolbar:
javascript:var mbid=location.pathname.match(/^\/release\/([a-f0-9]{8}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{4}-[a-f0-9]{12})/);if(mbid)void(open("https://rawgit.com/jesus2099/kepstin_magicisrc/%25231-support-pasting-multiple-isrcs/index.html?mbid="+mbid[1]));
And then go to your release and click the bookmarklet.
Then you can paste a bunch of ISRC to submit, like shown in the demos (animated GIF).