Roassal: Conditional X Axis Labeling

Question

In my chart, the x axis represents the Date. I'd like to only label the first day of a month. Specifying a number of ticks is problematic because they can be fractional.

What I'm looking for is something like:

someRoassalObject
  if: [ :point | point date dayOfMonth = 1 ]
  label: [ :point | point date mmddyyyy ]

(where points are my domain objects that respond to #date)

I did the following quick and dirty hack in the mean time:

b axisConfiguration
        labelConvertion: [ :x | (Date julianDayNumber: x rounded) mmddyyyy ].