Not cPanel specific, but I have a sub-domain with a catch-all set. Everything for @singleuse.. goes to my main mail account, so I can give CompanyX the address companyx@singleuse.. - their mail will get through to me, and if I start getting junk I can just block the address or set it to forward to the spam training account.
If you need to send mail to the company in question, as a reply to their mail or otherwise, make sure your client supports multiple identities and send out using that identity. Double-check though that your outgoing server doesn't add a "really sent by" header to outgoing mail. I find it very rare that I need to send mail like this though - most of the time the only email sent/received is the initial account activation instructions and any newsletter type mail they send out.
I'm not sure what you are meaning by "filter out addresses in the body of the email". If you don't want email addresses in the body of the email just don't type them there.