You can consolidate shipping via the app:
(Alternatively, you can tap the blue "trolley".icon on the main page, the one that looks like a flat trolley - like you'd use to move boxes around in a warehouse).
Tap the messages icon in the bottom menu bar.
Tap the blue delivery truck icon.
Then, scroll down to an item you know is in the warehouse already.
Tap the circle next to each item, for which you want to consolidate.
Tap the orange button to proceed to payment.
Tap the icon with a blue wallet, with some red cards peeking out.
Select your international credit/debit card, and you're good to go!
I just consolidated an order this way