Streamlined SaaS onboarding for AWS Organizations

Does anyone know if there is a way to streamline customer onboarding at the AWS organization level? This AWS blog post provided an approach limited to single-account use cases. I want to automate the onboarding process for a SaaS application in AWS organizations so that the role created for the SaaS is at the organization level, allowing it to assume a role across selected child accounts. https://aws.amazon.com/blogs/apn/new-aws-cloudformation-stack-quick-create-links-further-simplify-customer-onboarding/

EDIT

So, my thoughts about a possible workflow is as follows:

1. A Cloudformation template creates a role (super/org role, if you will) that can be assumed at the organization level. The role has the privilege to assume access to any child account.
2. A process discovers all child accounts and asks the owner which accounts should be onboarded.
3. The owner selects preferred accounts and onboarding proceeds.
4. On-demand onboarding can be done for any other account using the already-created role.