ADF bounded task flows can be opened in an external dialog and return values to the calling application as documented in chapter 19 of Oracle Fusion Middleware Fusion Developer's Guide for Oracle Application Development Framework11g: http://download.oracle.com/docs/cd/E17904_01/web.1111/b31974/taskflows_dialogs.htm#BABBAFJB  

Setting the task flow call activity property Run as Dialog to true and the Display Type property to inline-popup opens the bounded task flow in an inline popup. To launch the dialog, a command item is used that references the control flow case to the task flow call activity

<af:commandButton text="Lookup" id="cb6"
        windowEmbedStyle="inlineDocument" useWindow="true"
        windowHeight="300" windowWidth="300"
        action="lookup" partialSubmit="true"/>

By default, the dialog opens with a close icon in its header that does not raise a task flow return event when used for dismissing the dialog. In previous releases, the close icon could only be hidden using CSS in a custom skin definition, as explained in a previous OTN Harvest publishing (12/2010)

http://www.oracle.com/technetwork/developer-tools/adf/learnmore/dec2010-otn-harvest-199274.pdf

As a new feature, Oracle JDeveloper 11g (11.1.1.4) provides an option to globally remove the close icon from inline dialogs without using CSS. For this, the following managed bean definition needs to be added to the adfc-config.xml file.

<managed-bean>
  <managed-bean-name>
    oracle$adfinternal$view$rich$dailogInlineDocument
  </managed-bean-name>
  <managed-bean-class>java.util.TreeMap</managed-bean-class>
  <managed-bean-scope>application</managed-bean-scope>
    <map-entries>
      <key-class>java.lang.String</key-class>
      <value-class>java.lang.String</value-class>
      <map-entry>
        <key>MODE</key>
        <value>withoutCancel</value>
      </map-entry>
    </map-entries>
  </managed-bean>

Note the setting of the managed bean scope to be application which applies this setting to all sessions of an application.