I always play the main down wind when sailing 2 up with the kite. Gusts come, shifts come and the flow over the mainsail changes. Easing the main also effects the shape of the kite as the top of the mast moves and so moves the head of the kite.

So, to an extent (depends on how strong your mast is) you can play the mainsail to keep the telltails flying. Let everything out and the mast might break so take some care.

If I had a spare hand I would play the mainsail down wind single handed on the F16. I will sometimes change it downwind if I am not on the wire or when I gybe.