In the SAP business workplace is you attach an object to the decision task it will show up as link (under object and attachments), for example BUS2054 will display a link to a WBS calling transaction cj13 if I'm not mistaken, BUS2012 will display a purchase order etc.
Now you can create a new object and pass it to the task, pressing the object links runs the objects default method (defined in the object header) now the method can call a transaction or call link (using for example cl_gui_frontend_services).
This can be done also directly as an attachment to the task calling the transaction or link, but in my opinion it's easier to do so using an object.