Showing persentage as label

Hi,
I have a 100% stacked column (which shows bars in the chart( which show me bars (for each month) by deviding each bar in three parts showing the requests served in each month on time, not on time, finished early. Now if for one month i have 4 requests served on time, 4 early and 4 late, my bar is devided in 3 parts equally. If i select value to be showed as label, i can see it but i want to display percentage as label, in this example, i want to see 33% in each part of my bar. Can i do this without first calculating the percentage and mapping to my chart? if yes then how?

Thanks

Salman