Error Bars by Data Point instead of Series

I'm trying to put error bars on a bar graph of 3
series. But the data points are percentages and each data point has a different error range depending on the sample size. So far as I can tell, the error bar formatting tool only allows me to set the same error range for the entire series.

Is there a way to address each data point separately with regard to the error bars? Currently running 2004 on a Mac but I have just loaded 2008. I've tried in both and can't seem to make any progress.

Thanks,

Brian