openpyxl: Creating line chart with custom data labels / annotations

Question

I am trying to create an Excel line chart in openpyxl with custom data labels. Here is some example data.

from openpyxl import Workbook
from openpyxl.chart import (
    LineChart,
    Reference,
)
from openpyxl.chart.axis import DateAxis
from openpyxl.chart.label import DataLabelList
wb = Workbook()
ws = wb.active

rows = [
    ['Date', 'C1', 'C2', 'C3', 'SecondDate'],
    [date(2015,9, 1), 41, 30, 25, '2018'],
    [date(2015,9, 2), 41, 25, 30, '2019'],
    [date(2015,9, 3), 41, 30, 45, ''],
    [date(2015,9, 4), 41, 25, 40, ''],
    [date(2015,9, 5), 41, 35, 30, '2020'],
    [date(2015,9, 6), 41, 40, 35, '2021'],
]

for row in rows:
    ws.append(row)

chart = LineChart()
values = Reference(ws, min_col=2, min_row=2, max_row=7)
series = Series(values, title='C1')
chart.append(series)

dates = Reference(ws, min_col=1, min_row=2, max_row=7)
chart.set_categories(dates)

ws.add_chart(chart, 'A1')

I would like to plot C1 on the Date axis (as above). However, I would like to show the column 'SecondDate' as the data labels for the series C1 in the plot. Is that possible?