Dynamic JSF (2.0) commandButtons - set action with

I'm trying to add JSF <h:commandButtons> dynamically to my webpage, and so far I have them displaying, but I cannot set the action with parameters, like I could in a static page:
action="#{bean.function(parameter)}". (this is of course using EL-2.2)
Looking around I find that I have to create a MethodExpression, but this is obscure to me and I haven't been able to find much information on this. If someone could shine a light through the fog and explain how this can be done, it would be greatly appreciated.

EDIT: so now I have this

public void displayNode( String childName ){
//lots of messy code instantiating JSF components

if( activeEmployee.getParent() != null ){
        HtmlCommandButton parent = new HtmlCommandButton();
        HtmlOutputText parentLabel = new HtmlOutputText();

        parentLabel.setId("label" + count++);  //I really hate having to use count
        parentLabel.setValue( "Parent: " );

        parent.setId("Parent" + count++); 
        String parentName = activeEmployee.getParent().getName();
        parent.setValue( parentName );
        MethodExpression expression = createMethodExpression("#{tree.displayNode('" + parentName + "')}",
                                                                null, String.class);
        parent.setActionExpression( expression );

        newDiv.getChildren().add( parentLabel );
        newDiv.getChildren().add( parent );
    }

Use ExpressionFactory#createMethodExpression().

public abstract MethodExpression createMethodExpression(
                                      ELContext context,
                                      java.lang.String expression,
                                      java.lang.Class<?> expectedReturnType,
                                      java.lang.Class<?>[] expectedParamTypes)

Here's a convenience method:

public static MethodExpression createMethodExpression(String expression, Class<?> returnType, Class<?>... parameterTypes) {
    FacesContext facesContext = FacesContext.getCurrentInstance();
    return facesContext.getApplication().getExpressionFactory().createMethodExpression(
        facesContext.getELContext(), expression, returnType, parameterTypes);
}

The following action method examples:

public void submit1()
public String submit2()
public void submit3(String argument)
public String submit4(String argument)
public void submit5(String argument1, Long argument2)
public String submit6(Long argument1, String argument2)

can then be created as follows:

createMethodExpression("#{bean.submit1}", null);
createMethodExpression("#{bean.submit2}", String.class);
createMethodExpression("#{bean.submit3('foo')}", null, String.class);
createMethodExpression("#{bean.submit4('foo')}", String.class, String.class);
createMethodExpression("#{bean.submit5('foo', 0)}", null, String.class, Long.class);
createMethodExpression("#{bean.submit6(0, 'foo')}", String.class, Long.class, String.class);

Note that the EL expression is exactly the same as you would use in the normal view file.

Update here's an SSCCE which works fine for me with Mojarra 2.1.12 on Tomcat 7.0.27.

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml"
    xmlns:h="http://java.sun.com/jsf/html"
>
    <h:head>
        <title>SO question 12098611</title>
    </h:head>
    <h:body>
        <h:form binding="#{bean.form}">
            <h:commandButton value="add" action="#{bean.add}" />
        </h:form>
    </h:body>
</html>

@ManagedBean
@RequestScoped
public class Bean {

    private UIForm form;

    public void add() {
        String id = "button" + form.getChildCount();
        UICommand button = new HtmlCommandButton();
        button.setId(id);
        button.setValue(id);
        button.setActionExpression(createMethodExpression(String.format("#{bean.submit('%s')}", id), null, String.class));
        form.getChildren().add(button);
    }

    public void submit(String arg) {
        System.out.println("submit: " + arg);
    }

    public UIForm getForm() {
        return form;
    }

    public void setForm(UIForm form) {
        this.form = form;
    }

    public static MethodExpression createMethodExpression(String expression, Class<?> returnType, Class<?>... parameterTypes) {
        FacesContext facesContext = FacesContext.getCurrentInstance();
        return facesContext.getApplication().getExpressionFactory().createMethodExpression(
            facesContext.getELContext(), expression, returnType, parameterTypes);
    }

}

Unrelated to the concrete problem, all of above is a poor practice. See also How does the 'binding' attribute work in JSF? When and how should it be used?