I did it once, quite a few years ago now. It was a small AMHA show in Chickasha, OK. I used an easy-entry style cart with a 'pole'. Can't remember exactly how it turned out, but it wasn't too bad.
The biggest problem is for the course designer to set up obstacles that can physically be negotiated by a team as the team is wider than the wheel track of the cart. So, if you are expected to put the cart wheel between two boards and go a distance with the wheel between the boards, with a team, one of the horses is probably walking on the boards.
Some obstacles are no different, such us doing a pivot in a hulu-hoop. For something like weaving through cones, etc. , you just have less manuever room as the team is wider than just one horse.
Have FUN ! ! ! ! !