Thank you Alan. Are you suggesting that via DNS records I have DomainA.com "live" in the same place as DomainB.com, and then host the .htaccess on DomainB.com's hosting space?
So somebody requests DomainA.com, the DNS points to the hosting for DomainB.com, and then the .htaccess for DomainB.com can process the original DomainA.com request?