You can mark all of your data points as sliced, set innerSize and borderColor. For example:
series: [{
type: 'pie',
innerSize: '30%',
borderWidth: 1,
borderColor: 'rgba(0,0,0,0.5)',
data: [{
y: 23934,
sliced: true
}, {
y: 22503,
sliced: true
}, ...]
}]
Live demo: http://jsfiddle.net/BlackLabel/zpr4hygu/
API Reference: https://api.highcharts.com/highcharts/series.pie
Rotating data labels thread: Rotating dataLabels in a Highcharts pie chart