Forcing email headers

For various reasons, I need to force particular headers on all sent messages from the PP to my mail server.

The problem comes down to a client user, with a gmail account, for example, sending mail outbound through my mail server. Generally, you'd never allow such things in a tightly-run mta. Furthermore, my outbound relay (rollernet), would never let me send a message from my domain, with a gmail From: address. PP sends alerts as if they came from the PP user (or person).

The other issue is that, no matter that the email alerts state, "DO NOT REPLY TO THIS MESSAGE", people still do. I know, I know....

So I want to force the From: and Reply-To: fields to something of my choosing, like noreply@.... I'd also like to force the Return-Path:, so I can track bounces.

I looked through the Swift website, but couldn't dig up the variables.

Can I set this in our config/config.php somehow?

Thanks,
Josh