Nullable datetimepicker with a button

[Kysonel]

I found the nullable date time picker on codeproject.com.... but my
superiors would like to be able to click on a button in the dropdown
calendar to set the null value.

As an example for the button, there is the "Today" button in the lower
left corner of the calendar...

Is there a way that I could access the calendar to add a button? or
just a label to click on

please help ^_^

Kyson