How can I span a PageBlockSection into two columns in a one column display?

In the following code when I use columns="2" it spans two columns (you know the correct number here is four). When I use columns="1" it shows both fields in the first column.

How can show the label in the first half of the page and value in the second half of the page? I am also OK with any CSS gotcha as a solution.

<apex:pageBlockSection title="Span Entire Page" columns="1" collapsible="true" >
   	<apex:inputField value="{!attr.Width__c}"/>
    	<apex:inputField value="{!attr.Height__c}"/>
</apex:pageBlockSection>