Perfect you solved my problem :)
const referenceZscaling = {x:xMin , y: yMin, z: zdiff, name: "referenceZ", color: "transparent", toolTipContent: null}
const data = [{
type: "bubble",
showInLegend: true,
legendText:legendText,
legendMarkerType: "circle",
legendColor:"gray",
toolTipContent: toolTip,
dataPoints: [referenceZscaling,...dataPoints]
}]