A round ball, 1/4" or 6mm in diameter is just about equally effective as the "rice grain" method, imo. Ideally you will have a tiny bit of excess TIM squeeze out of the sides of the IHS, but the TIM won't quite make it to the corners. Maximizing contact from the IHS to the HSF/water block without creating an excessive mess is the goal. One might think pre-speading the TIM might be a good way, but this only traps air bubbles.