Custom email templates for access reviews

Hello, we need to send custom emails during access reviews and put some logic upon the email contents. How can we send custom emails when access reviews are started in okta. We are unable to use the Brand customization as it does not satisfy our requirements. Is there any other option for invoking custom emails for access reviews may be thru workflow, event hook or api?

In workflows we dont even see an event for access reviews starting. please suggest.