I think it will be a real challenge. I have two rear-facing carseats in each of the outer seats, and about enough room for the armrest in the middle. As you may already see, the middle seat seems to overlap the left seat. Even trying to put a carseat in the middle and hook it to the outer LATCH clips looks like there wouldn't be enough space to fit.
Too bad auto or carseat makers don't see this as a customer need or a sales opportunity.
http://spontaneoustriplets.com/2012/06/ ... s-one-row/ (Maybe it depends on what carseat you use, this guy got 3 across his small SUV)
http://thecarseatlady.com/triplets-tips ... for-twins/http://www.multimac.co.uk/home (looks cool, but UK company)