Custom day value in Calendar component

Hi.

Is it possible to add a handler to display own day value on the calendar (not only day number).
For example something like this (in groovy):

calendar.addDateRenderValue { date, eventsList ->
SimpleDateFormat sdf;
sdf = new SimpleDateFormat(“yyyy-MM-dd”)
return sdf.format(date)
}

Marcin

p.s. Sorry for my english