First you should make nginx listen to several ports, for example :80 :81 :82 and respond with different website on each. Google "nginx several ports", that's easy.
Second, you need to make tor "forward" several hidden service ports. I guess, by this in torrc:
HiddenServicePort 80 127.0.0.1:4986
HiddenServicePort 81 127.0.0.1:4987
OR, if this won't work, you can try to run several tor's as described here:
http://www.howtoforge.com/ultimate-secu ... y-with-tor
Please respond, I will be waiting for your feedback. This is interesting question.