I found this solution on StackOverflow a while ago while I was searching for something completely unrelated.
Whenever a user has Javascript disabled, the <noscript> tags come into play. Among other things, you can put some CSS code within those tags and it'll be fully processed. In this case, you could wrap your entire site into a specific <div> like this:
<div id="sitewrapper">
...your site content...
</div>
and then activate a special CSS definition for those that have Javascript disabled:
<noscript>
<style type="text/css">#sitewrapper {display: none;}</style>
</noscript>