Dood, that sucks. Pics are kind of unclear, is the screw broken, or just pulled out of place? If it's just pulled out of place, a good quality epoxy adhesive might be your easiest solution. There isn't really much strain put on those screws, so the epoxy might do the trick, but it's hard for me to tell for sure without being able to see it first hand. You'd need enough surface area for the epoxy to have enough to grab onto, if you know what I mean.
Either way, I'm sure you'd rather have it replaced, I really don't know what BKS is going to say about this one. They could claim 'installer error'. Best bet is to email them with pics and an explanation of exactly what happened. Be sure to tell them that it broke/pulled out as you were loosening the nut, not tightening it. That might be your only hope of getting them to give you a replacement.
Email them at cs@bks-tuning.com and CC a copy to rs@bks-tuning.com
tell them you were part of this group buy, and give them the same info you gave to me the first time around (name, shipping, etc).
I'll email them as well to give them a heads-up to expect a message from you, but I don't know that there's much else I can do for you on this one man.