EDIT: Because this keeps getting commented on, we all know that we shouldn’t do this. The question was how do I do it, not should I do it.
Add this into your for mobile devices. Then do your widths in percentages and you’ll be fine:
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no" />
Add this in for devices that can’t use viewport too:
<meta name="HandheldFriendly" content="true" />