I would publish the post and do the other person's contribution as a Quote.
you start a new line and use this symbol > and a space behind it. the is shows up like this:

this is a Quote

You have to do the formatting for each paragraph.
And I don't worry about cheetah anymore since they started to go for any duplicate content - shows up for our contests all the time. Still - use the quote option and that makes it easier for the other people to understand who wrote what.

Or, if you do the each writes one sentence, I would put the whole thing as a quote and each write some text that it is your entry and you did it with this person...