Hello,
Not sure why u want to schedule it manually, but what u can do is u can split ur scenario.
Disconnect sender with receiver proxy system. So, keep on dumping sender data (either in a form of a file or send it to PI server using receiver SOAP) and then in the second flow pull the data from temp PI location and send it to SAP.
Edited - U can ignore my reply becoz the same kind of answer is mentioned above.
Thanks
Amit Srivastava