I frequently blend at the tap just to try stuff (NHC is great for that), but you could just as easily do that with bottles if you were wondering what a blend would taste like.
In Germany, a lot of places had bottles of juice to blend with the weizens. Passion fruit juice, star fruit juice, banana juice, you name it. I even saw a girl drinking glass after glass of hefeweizen mixed with coke. She called it a diesel.