Try to understand your question, you want to have the stacked bar option into a meter chart?
I'am not aware of stacking measures into the meter chart, why can't you use the stacked bar chart for this?
May be this can be a workaround (although i just should use the stacked bar graph)
Create a graph, choose the meter option, add three measures: measure A, measure B, and measure C obtained from the measure math plugin (=A+B).
Then you will see your existant measures with next to them the "stacked sum measure".