In the survey we send to collect data for the shipment there will be an option to include them.
You can add it together with your current pledge when backing (adding the difference to the total pay amount) or you can pay for the add-ons via paypal when the campaign ends.
Please note also the increase of the shipping costs in your area according to the chart we have in the campaign.
Don't see the answer to your question? Ask the project creator directly.