I found a workaround since PayPal’s support said you couldn’t do this at all in their system. Go here to create a shipping label without an invoice: https://www.paypal.com/shiplabel/create/. It works with any street address in the modal window form, but the city, state and zip code needs to be accurate. Once you submit the form, you will be on a page where you can select your shipping type and information, and in the upper right corner you can calculate the postage cost without actually purchasing it. You can then take that total and add it back manually to your invoice. Hope this helps.
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