Well I see now :)
So this will be a problem, because I don't know any way how to call "save" (with same functionality as standard toolbar save button has) from codebehind.
As a workaround you can use two submit connections (one for save working copy another for submitting completed form). All your form fields must be NON compulsory (to 'disable' data validation and allow submit by first connection). Finally, when you are going to use second connection, you can validate all needed fields and raise validation errors if the're blank.
Anyway this is not the easy way and possibility to call this.Save() would be much more nicer.