Looking for a way to set up mail moderation using Entra dynamic group

Our organization is working on shifting from a hybrid AD-Entra environment to Entra only. We currently use mail-moderated dynamic distribution lists using Extension Attributes to set the rules for mass internal company emails. In conjunction with us migrating to Entra only, we are also planning to use an API integration to manage our Entra account creation and updates. This integration does not have the ability to populate the Extension Attribute fields. Because of these changes we will no longer be able to use the existing dynamic distribution lists we have, and we have not had luck finding a solution for it yet. Has anyone else gone through this or have any experience solving for this same problem?