When brushing the same data point twice it toggles the brushing state. Is it possible to change from "toggle" to "unite"?

When brushing the data twice (using SHIFT) and including the same data point it changes the brushing state from on to off. Is there any way to change this behaviour? I want it to be on even if I brush it several times. ( Anyway, why toggle is useful? Unbrush would be better!)