Hi Thales,
Can you elaborate your scenario a bit? What is the back-end you are using? Do you want to save the draft before initiating the request or save it for BPM activities once BPM or processes have been started? You can use CE tables for saving data temporarily. The below link may be helpful for you:
http://scn.sap.com/thread/2057022
Also, if possible please elaborate your scenario a bit.
Regards,
Kunal saggar