It's not like adding a spacer, it's much better as your not effecting the swing of the wheel when you turn. Keeping the wheel closer to it's original axis is a much better way of widening the track than adding spacers.
The bump stops are adjusted to the position that you require by loosening the tension rod to lower arm bolts and clamping it up where you want it. To get maximum angle on really extreme steering setups I actually modify the bump stop to travel even closer to the arm.