Is there a way for the data label values to appear on a chart only for
observations where the value is zero?

I have a clustered column chart where some values are zero. In such cases,
no column appears for these observations (i.e. a column of zero height). I'd
like to have a "0" appear right above the x-axis to indicate a zero value for
that particular observation. All other data labels should be blank
(including all the numbers would make the chart appearance too busy).

I realize I could simply add a text box with a zero. However, the chart is
frequently updated, and there may be some months when the value is not zero.
I'd prefer to have Excel automatically determine whether a data label should
appear.