Online Ad Test- Take Orders without Customer Being Charged

Hello,

We are looking to conduct a "dry run" online ad test to see how well our Squarespace site converts. To do this, we will be running paid ads on social media which will direct traffic to the site. We would then like to see how many customers actually go through the entire sales funnel and complete checkout. 

The trick is, we do not want customers to actually get charged as we are not ready to ship product yet. Instead, the ideal scenario is they complete checkout (using name/address/CC info) but after clicking "Complete Checkout" they see a message noting that we are currently out of stock and their card has not been charged.

Test Mode does not accomplish this as it doesn't allow the customer to enter their CC info. And zero'ing out the inventory prevents them from adding the item to the cart. 

Does anyone have ideas on how to best accomplish this?

Thanks!

DR