[Plugin: Contact Form 7] Setting "Return-Path"

I’m going on vacation now for a week or so, and am having a hard time getting my Google Apps mail vacation responder to work. The emails sent to me from CF7 have the user’s email set as the “From” and “Reply-To” address so I can easily reply, but Google’s auto-responder takes the “Return-Path” from the email header, which is some bogus email address being fed by my server (I’m assuming it’s some kind of php default). I’ve tried to add “return-path” to the additional headers section, but it doesn’t work.

I tested this:

<?php mail('to@mail.com', 'Subject', 'Body Message', 'From: from@gmail.com', '-f return-path@gmail.com'); ?>

and it works great. How can I get CF7 to mimic the functionality of the above PHP function? ie, adding the -f statement.

Thanks!

http://wordpress.org/extend/plugins/contact-form-7/