It is hokey at best. But here is what I had to do. i created a formula that looks something like this.
sum({amount to be summed},{column breakdown)/sum({amount to be summed}
Depending on your data, you may need a check for zero (do not want to divide by zero).
Also I changed the axis able to be a percentage and the data label to be a percentage. There was a lot of trial and error until I got it to work. Lots of luck.