I was wondering about adjusting the viewBox for this, so something like...
<div style="width:320px; height:480px;">
<svg id="svg1" width="100%" height="100%" viewBox="0 0 640 480" preserveAspectRatio="xMaxYMax"></svg>
</div>
jsfiddle http://jsfiddle.net/9zRR8/5/