So you want the form to include the SP ID?
I am not sure there is a way to get it in advance for a new item since it is generated when the form is saved.
What you can do I believe it perform two submits. A two step process should be undetectable to the user but accomplish your goals.
When the user submits, have it submit the new form once, then requery your data connection to get the ID number, save it in the form, and immidiately resubmit to sharepoint and update the form and then close or whatever. You would need to have the ability to overwrite the xml files in the library but I think that would be the way to do it.
You could also have it triggered earlier in the user process if you need the value sooner. The only issue if the user does not complete the form or if you have validation that would be needed before it could be submitted.