Workflow Attachment - Header and Line Level

Below is my requirement -

Table 1 < Header Table >  -- > Header Attachments

Table 2 < Line Table >  -- > Line Level Attachments

Using below code we are able to send multiple attachment in notification (Only for header level) .

wf_engine.setitemattrtext ( itemtype    => itemtype

                                         , itemkey       => itemkey

                                         , aname       => 'ATTACHMENT'

                                         , avalue       =>    'FND:entity=PA_PROJECTS&'

                                                         || 'pk1name=PROJECT_ID&'

                                                         || 'pk1value='

                                                         || l_project_id

                                          );

Can anyone any idea how to add header and line level attachments.