Hi Ryan,
There are two possible ways to alter the envelope sender email address of a message:
1- Masquerading Feature
This is a global setting and can change the Envelope senders and To:, From:, and/or CC: headers as well.
2- BCC/BCC-SCAN Message filter OR BCC Content Filter actions:
You can specity the Envelope sender email address with this action. This will create a totally new message but exactly the same as the original one. You may need to add second action as drop to not deliver the original message. This will only change envelope from and Return-Path and will NOT change From header.
Hope this will help.
Rehan