How do I make the search for recipients NOT execute until the user hits enter?

On Email compose our users start entering an email address to search for a recipient.

As soon as the first letter is entered the search kicks off... and it takes FOREVER to find matches, it's untennable.

I have found two things: 

• every search looks by first name, last name, full name and email address in EACH of the Users, Contacts, Leads, Prospects tables. 
• close to each additional letter typed kicks off yet another query for the entered partial string.

Our users NEVER enter names, they alway enter full email addresses. 

So I would like to cut the searching down by: not searching by all the variations on name, and not starting to search until the <Return> they is pressed.

I tried extending 

modules/Emails/EmailRecipientsService.php 

to restrict the ways it searches by commenting out a few terms:

        if (!empty($term)) {
        //    $wheres['first_name'] = $term;
        //    $wheres['last_name'] = $term;
        //    $wheres['full_name'] = $term;
            $wheres['email_address'] = $term;

Sadly appears that this can't be done in an upgrade safe manner (but MAN does it make a difference!)

But I still could not find a way to keep the queries from firing off before the user is done typing.

Any suggestions?

I would also get cake and cookies if I could sort the output by Contacts first, then Users, then Leads. :)

Thanks,

Francesca