BSB, there are a few of us smart enough to go through the cabin and close unused vents (or those at unoccupied seats) to try to help the temp before we go calling you guys up front.
However, it seems this technique is not well known as the last time I went through the cabin closing extraneous vents one of the other crew asked what on earth I was doing!!
So, that system only works if crew know to do it.
Honestly, on something as big as the 330 I haven't noticed it making much of a difference to the cabin temp, however the ' placebo effect' it has on the concerned pax is quite pronounced!
Works quite well on the 737 though, in case you were wondering.