Subscription apps cannot be currently integrated with Bundle Builder. Recurring payment apps (like Assemble, Recharge, or Paywhirl) - or other subscription service based apps - have conflicting code, which prevents Bundle Builder from operating correctly.
As a workaround, Bundle Builder offers inbuilt functionality which supports subscriptions for bundles created. For more information, see Purchase Options & Subscriptions.
Currently, it is not yet possible to integrate third party apps for this purpose. For more information, please see Draft Orders & App Compatibility.