Add asynchronous Javascript tag in ADF pages.

I have got a requirement to add asynchronous javascript to ADF pages and started using af:resource component but there is no option to add custom attribute for af:resource component. But here is the way..

Page content:

    <af:document id="d1">
      <af:form id="f1"></af:form>
      <af:clientListener method="sayHello" type="load"/>
      <f:facet name="metaContainer">
        <f:verbatim>
          <![CDATA[
          <script src="../scripts/tester.js" async></script>
           ]]>
        </f:verbatim>
      </f:facet>
    </af:document>

Application structure