It’s likely to be a little while until you get an official answer, given Easter.
However, I’m pretty sure there isn’t any way to do this - all playtest preorders are being fulfilled via Amazon, since the expected volume would overwhelm Paizo’s warehouse capabilities.
As I understand things, Paizo aren’t getting any significant numbers of the playtest materials shipped to them directly (so they can’t add it to our subscription shipments). Everything is going to one of Amazon’s shipping hubs to be distributed direct to the customer from there.
From the Preorder FAQ:
Can I combine shipping with subscriptions or other orders?
No. Pathfinder Playtest products cannot be shipped with any other products.
Hello Raisse,
It looks like Joana already answered your question. The playtest products will not be able to ship with subscription orders as they are being fulfilled through a different delivery service than we use for all our other shipping (Amazon Fulfillment).