In the head add this
//Include jQuery
<meta id="Viewport" name="viewport" content="initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no">
<script type="text/javascript">
$(function(){
if( /Android|webOS|iPhone|iPad|iPod|BlackBerry/i.test(navigator.userAgent) ) {
var ww = ( $(window).width() < window.screen.width ) ? $(window).width() : window.screen.width; //get proper width
var mw = 480; // min width of site
var ratio = ww / mw; //calculate ratio
if( ww < mw){ //smaller than minimum size
$('#Viewport').attr('content', 'initial-scale=' + ratio + ', maximum-scale=' + ratio + ', minimum-scale=' + ratio + ', user-scalable=yes, width=' + ww);
}else{ //regular size
$('#Viewport').attr('content', 'initial-scale=1.0, maximum-scale=2, minimum-scale=1.0, user-scalable=yes, width=' + ww);
}
}
});
</script>