I would expect airside sales in ZRH to be VAT free anyway as all flights from ZRH are international flights. They won't normally allow you to purchase items if you're connecting into GVA or LUG. Hence there's no need for a process of tax refunds.
Note that Schengen has nothing to do with tax and customs. It's about free movement of persons, not goods. Switzerland is part of the Schengen agreement, hence no passport checks on flights within the Schengen area, but is not part of the European customs union, so it's a little island within Europe in that respect.