I was researching that when I found this thread. I'm trying to tune my front suspension and can't get negative camber on one side. Someone suggested adding 1/8" washers between the ball joint casting and spindle to tilt the wheel in. I'm thinking about trying it.
If that doesn't work you can get ajustable upper control arm, that's what I did. Once you have those on there the adjustment is prettty much limitless!!!