This issue is now becoming urgent as the UK is going to leave the EU. Any sales done outside of the UK will need to have the VAT removed. Shopify needs to urgently work on a solution because all British ecommerces will face the problem.
Lenka from Sufio here!
It's been quite a while since you posted this and you might have figured this out already. In any case, I'd still be happy to share more details.
With Sufip, you can capture the VAT number at the Customer registration page / Customer Account page / Cart page or Checkout (only for Shopify plus). It is also possible to add a VAT validation.
Once there is a VAT added to the order details, the prices will be VAT exempt. Does this answer your question? Please, feel free to reach out to firstname.lastname@example.org if you have any questions.