If I have read this correctly, you could just set up a domain alias through your server.
Most hosting control panels will allow you to do this.

You will of course have the duplicate content issue, and probably some complexity with tracking conversions through your analytics program. But a domain alias will allow you to have the exact same website on a different domain name.
Then, through your programming code, just read the domain that you are on and show the appropriate content for that domain.

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