While your order is still on wait list status, you cannot add a payment plan to it. However, if it converts to a confirmed order, you may then add a 3-month payment plan!
Simply go to the My Orders section of the website within your account and select the formerly wait listed order that you would like to add a payment plan to. Click the text that says "ADD PAYMENT PLAN" beneath the item.
Next, select "3 Months + final payment" from the drop-down menu on the following screen and click "SAVE".
Congratulations, your new payment plan has now been applied to your converted wait list order and will be displayed on your order page!