Setting both bar thickness and spacing in bar charts

[adatti]

Is there a way to set both the bar thickness and the amount of space between the bars in a bar chart? I want to have specific values that do not change. For instance, I would like the bars that are 30px thick and spaced 10px apart. The categoryPercentage and barPercentage both seem to get canceled out after I set a specific barThickness in pixels, and there is no option to set the spacing explicitly.