public class CIMPointCloudStretchRenderer : CIMPointCloudRenderer, System.ComponentModel.INotifyPropertyChanged, System.Xml.Serialization.IXmlSerializable  

//Must be called on the MCT
//var pcsl = ...;

//At 2.x - var fields = pcsl.QueryAvailablePointCloudRendererFields(
//                           PointCloudRendererType.StretchRenderer);

var fields = pcsl.GetAvailablePointCloudRendererFields(
                         PointCloudRendererType.StretchRenderer);
var stretchDef = new PointCloudRendererDefinition(
                          PointCloudRendererType.StretchRenderer)
{
  //Will be either ELEVATION or INTENSITY
  Field = fields[0]
};
//Create the CIM Renderer
var stretchRenderer = pcsl.CreateRenderer(stretchDef) 
                                   as CIMPointCloudStretchRenderer;
//Apply a color ramp
var style = Project.Current.GetItems<StyleProjectItem>()
                                .First(s => s.Name == "ArcGIS Colors");
var colorRamp = style.SearchColorRamps("").First();
stretchRenderer.ColorRamp = colorRamp.ColorRamp;
//Apply modulation
stretchRenderer.ColorModulation = new CIMColorModulationInfo()
{
  MinValue = 0,
  MaxValue = 100
};
//apply the renderer
pcsl.SetRenderer(stretchRenderer);