I have a knack for finding the Rube Goldberg way of doing things sometimes, this may be one.
I'm not familar with sharepoint, but I'm assuming it has a primary key field like that in access. If thats the case:
Have a repeating section bound to a table in access or something. Make sure theres an extra field in the table, call it DummyPrimaryKey. Set the default value to position().
Make a rule in this field that sets the values of the other fields. Should look something like:
Field: AccessField1
Value: SharepointField1[SharePointPrimaryKey = current()]
Next, extract the form files. Open up the "schema.xsd" and find the number of minimum occurences to that table. Change it to something large or the number of entries in your sharepoint database.
Save it, close it, run it. See if it works.