It's possible, but requires a bit of source level modfications. PrimeFaces API provides the mentioned functionality via
Axis.setTickFormat, and you can reference Axis instances by overriding
BarChartBuilder.createModel for instance.
There are multiple ways to achieve this, but the important part is obtaining a reference to the chart model somewhere and modifying its axes configuration before it's returned to the JSF side.
Please let me know if you need further help.
Cheers,