right=1Freeze

<s:SkinnableContainer skinClass="scrollableskin">
        <s:Button right="-1"/>
    </s:SkinnableContainer>

...where scrollableskin is

<?xml version="1.0"?>
<s:Scroller width="100%" height="100%" xmlns:fx="http://ns.adobe.com/mxml/2009" xmlns:s="library://ns.adobe.com/flex/spark">
  <s:Group id="contentGroup" left="0" right="0" top="0" bottom="0" minWidth="0" minHeight="0">
    <s:layout>
      <s:BasicLayout/>
    </s:layout>
  </s:Group>
</s:Scroller>