custom_comments app: __init__.py

from custom_comments.forms import SimpleCommentForm

def get_form():
    return SimpleCommentForm

custom_comments app: forms.py

from django.contrib.comments.forms import CommentForm

class SimpleCommentForm(CommentForm):
    class Meta:
        exclude = ('name', 'email', 'url')

settings.py

INSTALLED_APPS = (.... 'custom_comments' ...)

COMMENTS_APP = 'custom_comments'

template.html

{# content is a object #}

{% render_comment_form for content %}