Notifying approvers about a PIM approval request without their email property

In Azure AD PIM, we aim to notify the approver when a user request to activate their eligible role.

I think by default Azure use the email property of the approver for sending an email for notification. However due to various reasons, we cannot use that property and have to leave the property empty.

Therefore we are not sure about how to notify the approver when the request is sent.

Are there any alternatives to notify the approver about the request bypassing the use of the email property?

Specifically we have considered creating a security group for the approver and set the property "select approver" property as that group in PIM role setting.

However no member in that group has an email property in their user attribute.

Any suggestions or insights would be greatly appreciated.