wouldnt really be too hard.. if you were going to do it i would recommend tracing them farther down into the dash and blocking them off as far down as you can. if you block them off right behind your dash, whatever you used to block them is still going to get hot or cold from the climate control. keep in mind if you have the same amount of air coming from your fan to a lower number of vents you are going to get more noise from your vents because the air speed will be higher