Selective Message History Forwarding in Service Center

Hi CCC,
we already have the setup in place that allows the message history to be carried over in each reply on Service Center.
The issue is that our client would like to be able to reply to the last message (in order to forward the previous conversation) to another user, and then, if after this forwarding they reply again to their own customer via SR, they would like the forwarded message to the third party not to be included in the message history received by their customer.

The forwarding of the conversation history doesn't necessarily have to be done via "Reply All" — if "Reply All" always includes the full message history, any other solution that satisfies this requirement would be perfectly fine for us.