If these are PDF invoices and are kept for you to access, then you could do it in an even simpler way and just record daily / weekly takings rather than individual sales. If you can grab a total each week of the 20% and 0% VAT sales, you could then just input them into QuickFile as a generic client (e.g. “Weekly takings” or “Online Shop”). The original PDFs would be the record to show where the money came from should any queries be raised.
These guides may be of help with this:
Obviously, the choice is yours - but it’s an option! 
Other than that, it’s not currently possible to import multiple lines through the import tool, but you may wish to add your vote to this feature request: Multi-line invoice importing
Hope that helps, but please don’t hesitate to let us know if you have further questions