Best way to let Django SplitDateTimeField accept an empty time field?

I like to have the date part in the SplitDateField, but the time part - if left blank - defaults to some value ('00: 00: 00 ').

I am currently a monkey patch that is used in the Fields clean () method. Is there a better way to do this? A more "Django-like" way?

Looks like this now (in forms.py file):

def mp_clean(self, value):
    # time is in value[1] of a split-datetime field:
    field_value = value[1]
    if field_value in self.empty_values:
        value[1] = '00:00:00'
    return self.mp_original_clean(value)

class MyModelAdminForm(forms.ModelForm):

def __init__(self, *args, **kwargs):        
    super(MyModelAdminForm, self).__init__(*args, **kwargs)
    that_field = self.fields['that_field']


    if isinstance(that_field,forms.SplitDateTimeField):
        that_field.mp_original_clean = that_field.clean
        that_field.clean = types.MethodType(mp_clean, that_field)