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It is most likely possible to implement this via plugins, but here is an alternative approach that gives you the exact same behavior.
Basically, you use an external custom tooltip positioned in the middle of the chart that is triggered when a chart segment is hovered.
Here is the relevant code
Chart.defaults.global.tooltips.custom = function(tooltip) {
// Tooltip Element
var tooltipEl = document.getElementById('chartjs-tooltip');
// Hide if no tooltip
if (tooltip.opacity === 0) {
tooltipEl.style.opacity = 0;
return;
}
// Set Text
if (tooltip.body) {
var total = 0;
// get the value of the datapoint
var value = this._data.datasets[tooltip.dataPoints[0].datasetIndex].data[tooltip.dataPoints[0].index].toLocaleString();
// calculate value of all datapoints
this._data.datasets[tooltip.dataPoints[0].datasetIndex].data.forEach(function(e) {
total += e;
});
// calculate percentage and set tooltip value
tooltipEl.innerHTML = '<h1>' + (value / total * 100) + '%</h1>';
}
// calculate position of tooltip
var centerX = (this._chartInstance.chartArea.left + this._chartInstance.chartArea.right) / 2;
var centerY = ((this._chartInstance.chartArea.top + this._chartInstance.chartArea.bottom) / 2);
// Display, position, and set styles for font
tooltipEl.style.opacity = 1;
tooltipEl.style.left = centerX + 'px';
tooltipEl.style.top = centerY + 'px';
tooltipEl.style.fontFamily = tooltip._fontFamily;
tooltipEl.style.fontSize = tooltip.fontSize;
tooltipEl.style.fontStyle = tooltip._fontStyle;
tooltipEl.style.padding = tooltip.yPadding + 'px ' + tooltip.xPadding + 'px';
};
And a working example as well.
Source:stackexchange.com