There is no equivalent task you can model in your process that won't create an instance. Although it is possible to automatically end your process instance from within your task flow and then not have the taskflow return an outcome, a better solution would be the global/external applications links you can setup in the workspace. There is a sample documented for this, although you would somehow want to check the roles of your users to show/hide the links probably. These links would then go to stand alone ADF taskflows where you can present anything you would like without a process instance.
See the example at http://java.net/projects/oraclebpmsuite11g/downloads/directory/Samples/bpm-CustomizingWorkspace/