OctaGate Switch lets you add headers to both the request and the response headers, on a per domain basis. This is only available on the Enterprise Edition.
Add to/replace request header
Add to/replace request header will either add the lines you enter in the textbox, or update the value of the lines in the header if they already exist.
Add to/replace response header
Add to/replace response header will either add the lines you enter in the textbox, or update the value of the lines in the header if they already exist.