Hi Nick,
So, since i've posted that thread I went many times to kite in Rio and first of all, I would not at all recommend you to leave your kitegear on the beach. That being said, they are couple bar-clubs along the beach that provide great service like air pumps and an area to leave your gear, but it does not come cheap. Between 50 and 100 reals a day. However, every time I go, I would just consume after my session and I've never really been asked to pay the fee...
The main spot is located in Barra da Tijuca, and the wind usually kicks in the late afternoon. The buses are easy to find, they can just be really painful with the heat in the summer, but at the time you'll be going it will not be that hot... However they can be much faster than 1.5h, like 40 min if no traffic ; you have to stop at the white bridge after the tunnel. You'll just have to walk from there like 5 mins. Just take a pullover for the return, because the AC is gonna kill you !
About the spot, its not the easiest... If you are thinking about unhooked stuff, don't expect too much, the wind is harshly steady and waves get sometimes pretty big and as it's a short break, can be pretty devastating. However, with a surfboard, it's great fun !
I hope you'll enjoy,
Cheers,
Robin