Here is the way I would do it. Let's say, to expand your example, you had the values 3, 25, 32 in A2:C2. In A1, place this formula:
=A2&"("&TEXT(ROUND(A2/SUM($A$2:$C$2),2),"0%")&")"
The meat is the TEXT(ROUND(A2/SUM($A$2:$C$2),2),"0%"). This will divide A2 by the sum of the three columns and round the answer to two decimal positions. The TEXT function has a format string of "0%" which will yield the 5%. The rest of the formula is simply concatenating the original value to be graphed and the parentheses.
Copy the formula in A1 to B1 and C1. You should now have your labels of 3(5%), 25(42%) and 32(53%). Select A1:C2 and insert a bar chart.