a.py

class MortgageForm(ModelForm):
    class Meta:
        model = Mortgage

    def __init__(self, *args, **kwargs):
        """
        Custom init method

        """
        import ipdb
        ipdb.set_trace()
        super(MortgageForm, self).__init__(*args, **kwargs)
        commentable_fields = []
        if hasattr(self._meta.model, "_commentable_fields"):
            commentable_fields = self._meta.model._commentable_fields
            for i, field in enumerate(self.fields):
                if field in commentable_fields:
                    cf = forms.fields.CharField(label='comment_%d' % i)
                    cf.is_hidden = False
                    self.Meta.fields.insert(i+1, cf)

class MortgageAdmin(admin.ModelAdmin):
    inlines = [
            # inlines here
            ]
    form = MortgageForm
    fields = [
            # field list here
    ]