You can do that with constraints when making your axis,
CPTXYAxis *x = [self _makeDefaultAxis];
x.coordinate = CPTCoordinateX;
x.axisConstraints = [CPTConstraints constraintWithLowerOffset:0.0];
x.tickDirection = CPTSignPositive;
// ...
CPTXYAxis *y = [self _makeDefaultAxis];
y.coordinate = CPTCoordinateY;
y.axisConstraints = [CPTConstraints constraintWithLowerOffset:0.0];
y.tickDirection = CPTSignPositive;
// ...
CPTXYAxis *y2 = [self _makeDefaultAxis];
y2.coordinate = CPTCoordinateY;
y2.axisConstraints = [CPTConstraints constraintWithUpperOffset:0.0];
y2.tickDirection = CPTSignNegative;
// ...
CPTXYAxis *x2 = [self _makeDefaultAxis];
x2.coordinate = CPTCoordinateX;
x2.axisConstraints = [CPTConstraints constraintWithUpperOffset:0.0];
x2.tickDirection = CPTSignNegative;
Which gives something like,
So also show the labels you need to adjust the padding etc.