I love taking my son (or daughter, wife, dogs) out on our TI. He's almost 13, so older and heavier than your son.
As others have mentioned simply tie the furling line to the main and your set. Everything is easily manageable from the rear seat. When my wife is with me she prefers the rear seat so that she doesn't get as wet.
I have the tramps but have never set them up while on the water. I get everything setup while on a trailer, then slide it in the water.
You can sail solo from the rear seat just fine but I have found that a 5 gallon water bag
http://www.amazon.com/Reliance-Products ... +water+bag in the front footwell does wonders for the ride in the new hull. It lets the bow stay a little lower and actually cut into the waves vs riding up on them and slamming down on the next wave.
If you're on a lake with short period waves from wind and boat wake a little weight in the bow is great.
I also have played with sitting in the front and adding the water bag on the rear storage area and that works great too.
Heres a video on Lake Lanier just north of Atlanta. The video gets a little wavy in places thanks to YouTubes stabilization..
https://www.youtube.com/watch?v=JbBGv9Txm_gI love the TI, it was initially a tough sell to my wife... But now she is a big fan.