This may be a bit tricky to do but I assume you want people to kind of work together, get in touch, communicate.

So how about, to start the sequence, you pick a post that is less than 7 days old, written by someone who comments on this post (you will use the last post every time you create a new challenge post). You put the link as a comment to your own post so we can vote for it.

You upvote the post you picked and add a comment, telling them they are nominated in your new post. Then they have to do the same thing they have to find a post of someone else who commented on that last post and add a link to that post as a comment, and add it in a comment to your new post, and so on.

Others who are not (yet) nominated can take a look at those posts, hopefully upvote it, and if they really like it they can upvote the comment. The writer of the comment with most votes after 7 days wins. Well if that would be you, I guess the runner up will win :)

The good thing about this system will be that we read more of eachothers posts. You will get more comments, hopefully, because only those who have commented on the last post can be nominated in the new one.

But also you can spread the word of Steembasicincome because there will be comments added to posts telling about your challenge.

An example:
You pick post X of mr X. You write your challenge post, and add a comment to your challenge post saying you nominate post X of mr X
Next thing you do is go over to post X, upvote it, add a comment to it telling about your challenge and that they are nominated. And that they should nominate someone else now.

Mr X looks at the last post, picks ms Y as nominee and looks for a good post on her blog, post Y. Then mr X comments on your challenge post that he nominates post Y written by ms Y. Then Mr X goes to post Y, upvotes it, comments on it that ms Y has been nominated and now has to nominate someone else.

Too complicated ? :)