Currently the legend aligns the text to the left. I.e (-- indicates item label and in most cases would be just different colors.
___________________ [-- Legend
You can set useHTML and then define width and text-align:
http://jsfiddle.net/5gjfW/2/
.highcharts-legend-item span { width:70px!important; text-align:right!important; }
http://api.highcharts.com/highcharts#legend.useHTML