Hi. No, unfortunately there's no way to turn safe frame off in IR, and there were non either in older versions. But back in alpha versions IR was always showing the full viewport - with no option to turn safe frame on, except from doing a Render.
I too would like the option to use IR with and without SF, and a simple way to do it could be, that IR always followed the viewport setting. Meaning: if SF is on in the viewport, then SF is on in IR, and if SF is off in the viewport, then SF is off in IR.
Hope this will be implemented some time :)
Edit: beaten by romullus :) But basically the same answer.