There is easy solution to that old mirror problem: multiple domains and SSI.
Couple of years ago I asked my host to put all my domains (I'm still with virtual hosting) in same server and in same folder. Then I asked them to do me a global folder named 'ssi', in the same root folder where all my domains are, and put that global folder to work in all domains. They did that.
OK, now I can have all my content somewhere in global 'ssi' folder. Every domain sees that folder as part of their own root folder, like that:
http://www.mydomain.com/ssi/
Now you just build your free site in one domain, put there the recips you want in index.html and then you can build that same site to other domains. Just change things a little bit for SEs. You can also use different sponsors if you wish in different domains if you want. You can also name all the sites differently if you want. I often buy content that is good in multiple niches.
That way you have no mirrors, no doorway pages. You can rotate domains, like 1st site for big boys in domain 1, next site for them in domain 2 etc.
Everybody is happy, because you aren't cheating in any way. Every one of those sites are perfectly good site. Everybody have traffic.
I hope this helps. There is good SSI tutorials on net for those who haven't tried it yet, and I'm ready to help, just mail me.
SSI is easy to use. I'm one of the most crappy tech persons in this whole wide world, but I understood it clearly when I read one tutorial, so if I can learn it, everybody can.