Request for advice: seminar style class with 30 students?

So I am teaching a new course this coming semester. It is on the topic of evaluating social programs (surprise, surprise) and will be a scaled-up version of a class that I taught twice at Western Ontario with about 10 students each time and have taught twice at Michigan with five and then with 16 students.

In thinking about how to scale up the class to 30 students from 10-15 there are two main issues. The class is based mainly on student presentations of actual evaluations drawn from the literature followed by class discussion. With 10-15 students every student can present at least once, there is enough time for every student to participate in the discussion at least a bit and the threat of public embarrassment if I "cold call" on a student during the discussion suffices to insure that most students read the papers most of the time.

With 30 students, there are not enough class sessions in a semester for every student to present at least once (even without accounting for the fact that I lecture for the first couple of weeks to provide a common foundation of knowledge). One option to deal with this is not to have all students do presentations - those who do not could, say, participate by being formal discussants or simply have their grade based entirely on the paper and on their participation in the discussions. Alternatively, I could have the student do the presentations in groups of some sort, such as pairs or even trios. If I do down that road, I then have to come up with a way to form the groups. Unlike the honors students at UWO, who took all of their classes together and knew each other pretty well, most of the students in my class will not know any of the other students well, so letting them form their own groups is not really feasible.

With 30 students, I also need some other mechanism to make sure that all of the students read the papers, as it is no longer possible for all the students to talk about each paper during the discussion or for me to cold call enough student to get the embarrassment threat level up high enough to guarantee that they will do the reading. Options here include having each student write a one page summary and comments about each paper, which would be graded by the teaching assistant (perhaps only at random) and having each student prepare discussant remarks, with the discussant then chosen at random during class. The problem with random discussant assignment is that some students will get picked more than once and some not at all. If I just randomize the order, then students who do their discussions early know that they do not have to prepare the rest of the time.

So I am puzzled as to the best course on both fronts. Suggestions welcome, either in the comments (open but totally unused for several months now) or by email.