Ahh... then you're doing this for a friend. As I said, that's completely different, no pressure you're not a hired gun getting paid for professional quality work.
I think there's still probably quite a bit of pressure, but OP shouldn't be as stressed about producing the kind of work as The Strobist or McNally would turn out.
That said, get (or more likely rent) a couple of speedlites, and either use a master mounted on your camera or some RF triggers and put them on stands a decent distance away, at approximately 45 degree angles from the group facing inwards. It'd be better if you could get 2 at each point, one high one low and shooting through or bouncing from an umbrella or octo-box. It'll eat power, but you'll get much more even light. Don't feel you need to be at ISO 100 either. With some decent light, ISO 400 or even 800 will be perfectly acceptable. I'd also go to f/5.6 or 6.3 to increase your DoF. Especially if you have people ranked 3 deep. Last, don't use your 17-40 at 17mm please. At least 24mm, maybe creeping up towards 30-35mm if you have enough room.
Actually, looking at it you will have a decent number of speedlites. If you can get some RF triggers (most also have a PC out connection so you can use 1 per pair of speedlites) that'd make it a lot easier and more reliable to trigger. If at all possible, I'd recommend showing up quite early, getting a good look at the location and then getting your friend (or someone really) to stand at various locations of where the group of people will be while you shoot them and adjust your lighting and power settings. Also use a few bits of gaffers tape to mark the edges of where people need to stand. That way, when you actually need to get shooting you'll just have to herd them into the target area, make sure you can see everyone's face, get 1 or 2 test shots and then get 1-2 minutes of a bunch of shots. Make sure you talk to them, don't just go bang! bang! bang! Tell a joke, or talk with your friend ahead of time and tell him you're going to make fun of him a bit to get a laugh. That'll help get them to relax and you'll get much better photos that way.