JSF 2 - How can I get a context-param value from web.xml using JSF EL?

I would like to declare some constant values used by my JSF 2 webapp inside the web.xml file like so:

<web-app>
    <context-param>
        <param-name>myconstantkey</param-name>
        <param-value>some string value</param-value>
    </context-param>
</web-app>

Getting these values from inside a backing bean is easy enough:

FacesContext ctx = FacesContext.getCurrentInstance();
String myConstantValue =
    ctx.getExternalContext().getInitParameter("myconstantkey");

How do I achieve the same thing from inside a Facelets page using JSF EL to get the value?