Your VF override page can have some logic in it that would add a URL parameter to the page based on what it finds about the device being used to see the page. Then your conditional rendering could be done based on that URL parameter. Below is a quick and dirty example.

apex:page

</apex:page>

You could do this to conditionally render sections of your page based on device, viewport size, whatever else is reported back from the browser in this page.

Thanks for the reply Rob, another question I got is that, what if I need to render a button and hide if the user is logged in via salesforce1