I've also been looking into this. I don't think the Adsense responsive code gives you an option to not have the ad at specified widths, just to change the dimensions.
I think the easy way might be to use divs with display:none depending on the browser width, however I get the feeling that putting Adsense in an hidden elements may contravene Google's terms so it needs to be a way that doesn't include the Adsense on the page source but be hidden from view.