I have a T900 with my son as stroker, he turns 5 this month. I have a rear rack on the tandem that fits my child carrier so I attached it - here is what it looks like:
t900-bike-with-baby-seat_2.jpg
I guess your stroker would have a backrest, but I think it would make the rear very unstable - make sure you can support the weight. Also notice the baby seat isn't quite level. You may have to manufacture something to attach the front of the rack to the bike - there isn't much room. I am planning to put my younger kids in my trailer, I don't think I would use the baby seat unless it was an emergency. It might not be good if the kids started fighting!
I had to attach a 2x4 to the pedals for my son (3'6") to reach comfortably. I will be adding a heel strap to better keep his feet on the pedals. The crank shortners where $50 off eBay. I was told that you cannot use a child stoker kit on this bike when I bought it.
As a side note my stoker just loves the bike, I got him some biking gloves, a bottle cage and a bell. I have a handlebar mirror that also allows me to see him behind me, which is nice.