You will only be able to bind the repeated file field in the multi insert interface, there is no choice to insert an alternate value. It might be possible to get your DFP upload bindings inserted with the multi insert but it would require making changes to the WA_AB_getLoopedFieldValue function call. This is not something I would suggest doing unless you are experienced in ASP VB coding.
The alternative would be to use update server behaviors to go back and update each of the records to add in the bindings you need from the available upload bindings.