Jake,

You can prevent the chart to reserve space for the hidden axes by setting negative values to the axis margin as shown in this code snippet below,

axisY:{
    title: "",
    tickLength: 0,
    lineThickness:0,
    margin:-4,
    labelFormatter: function(e) {
      return "";
   }

If the solution suggested doesn’t fulfill your requirement, kindly create a JSFiddle with your use case so that we can understand your scenario better and help you out with an appropriate solution.

—
Tony Antony
Team CanvasJS