We do not have any documentation for using the update like this. The problem is that the DFP upload server behavior is just not compatible with the multi insert or multi update server behaviors. Due to this you will not be able to insert the image information for each record when the record is inserted. To get around this you would add in update server behaviors on this page to go back and update the records that you just inserted. In order to update the record you will need to have an identifier for that record, so you would need to use the values from the form as the field to base the update on rather than the id. This is not a simple scenario to deal with and will require some extra effort to get into place. Please post back with any specific questions about any part of this and I will do my best to explain it and help you get it going.