Multi-Tenant App Needs Certificates

We are working on a multi-tenant Whitelabeled app. Currently we can build for it, but there are limitations to customizing the domain name since the app settings only allow 1 custom domain AND there is no way in the system to handle adding custom domain names as a Subject Alternative Name on pre-existing certificate for the app. It would be great to be able to truly whitelabel a web based app and handle this by either allowing for a custom third-party certificate solution or being able to update the existing cert for the app domain name.