Compose Email - Select Recipients - Customize Recipient Type dropdown list

When you compose a new email and click the To button, a dialog appears to select recipients.
There is a field called Recipient Type that has a dropdown list.
I want to customize this list to show only Contacts as a choice.

I’ve gone down the path of creating a custom controller and creating several custom files (Emails.php, EmailUI.php, index.php and probably a couple more).
I thought I had it nailed by modifying the arrays in EmailUI.php that list the dropdown options, but that did not work because the default Email constructor is called from Email.php instead of the one in my CustomEmail.php file (because I renamed the constructor to CustomEmail after sublcassing the original Email class), even though several other functions in the CustomLEmail.php file are called as expected.

At this point it seems like this is getting way to complicated for something that should be relatively simple. What is the right way to customize the items in the Recipient Type dropdown list ()?

Thanks,
Glenn

I finally got this to work by editing one of my calls to my custom code with the correct name.
However, this seems like way too much work for this.

Is there a simpler method?

Glenn