From the physical side of the problem, it doesn't matter if you hold the ball lightly on your fingertips or you have it on the palm - because if you have it on the palm, what will create the spin is NOT RELEASING all your fingers at the same time. (If we take that the hand moves straight upwards, there's no possible spin component coming from there, BUT if one side of the ball brushes your thumb a split second BEFORE or AFTER it brushes the remaining fingers, that spins it, however lightly.)
So, if you want to toss a perfectly spinless ball holding it in your palm, the point is in the finger release action.