How to set css class of a label in a django form declaration?

I'm using django-uniform and to use some uniform features, I'm looking for a way to add css class directly from form declaration (for independents widgets).

(as a bonus, here my reusable read-only home made mixin snippet...)

from django import forms

def _get_cleaner(form, field):
    def clean_field():
        return getattr(form.instance, field, None)
    return clean_field

class UniformROMixin(forms.BaseForm):
    """
    UniformROMixin, inherits to turn some fields read only

      - read_only = list of field names.
    """

    def __init__(self, *args, **kwargs):
        super(UniformROMixin, self).__init__(*args, **kwargs)
        if hasattr(self, "read_only"):
            if self.instance and self.instance.pk:
                for field in self.read_only:
                    self.fields[field].widget.attrs['readonly'] = True
                    self.fields[field].widget.attrs['class'] += "readOnly"
                    # here I would like to set css class of the label
                    # created from the self.fields[field].label string
                    setattr(self, "clean_" + field, _get_cleaner(self, field))

My only way for now is to add a bit of javascript on my generic form template and add classes manualy.

Any brillant idea?