The not very interesting story behind my user name is that there was a site where I used to comment and I used to be just plain Mo, until a troll showed up and used that for a while as their screen name. So I changed mine to Mo (The Good One), but then I realized that another perfectly fine Mo was also around (it's way too common a name), and when I tried to change it again, the hosting site got its wires crossed and it was a crap shoot which of the three names would end up showing up each time I posted. Hence, I ended up deciding that Mo' Mos = Mo' Problems, changed it to that! and it actually stuck.
And to stay on topic, no, then I don't know how you could challenge the computer on a specific quiz. But, unless you want it to count towards a badge, even without a challenge you would still know whether you beat the computer - since, unless I'm completely wrong here, the computer score in a challenge equals the average of users' correct answers for that game, and you are given the chance to see how you stack up to that at the end of every quiz.