ION AUTH send email using Amazon SDK API

I want to use Amazon SDK API instead of SMTP I have created Amazon Access Key and Amazon Secret Key from Amazon and now implemented in my project it working fine as where I have to send email I replace $this->email->send() with the library function I have created to send email which is using Amazon SDK.

Now when I reached the page where the user does signup, I found that the code is of ION Auth and not sure how to implement this for ION auth so that it will pick my library function to send email instead of CI SMTP. Please help how to do it. How I would able to send Activation email using Amazon SDK instead of CI SMTP settings