Just create one portal per website.

Then give it an alias URL for each way that you want to use it.  I have a copy on my local machine and an exact copy (both code base and database) with my hosting company.
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I have aDNN installation that hosts several totally different websites.  For each of them I have three aliases.  Suppose the actual site on the internet is tangodancing.com, then I have the following three aliases.

http://mymainwebsite.com/tdancing (child portal) the public could see this if they knew it existed
 - I do this just so I can log into the parent as host then get to all the portals without having to log into them separately.

http://tangodancing.com  (what the public sees) - parent portal

http://localhost/tdancing  child portal of localhost - this is how I access the site copy when it is on my local machine so I can test upgrades, new modules etc.