class FeatureForm(forms.ModelForm):
    offer = forms.ModelChoiceField(queryset=Offer.objects.all(), required=False
        )
package = forms.ModelChoiceField(queryset=Package.objects.all(), required=False
    )

def __init__(self, *args, **kwargs):
    super(FeatureForm, self).__init__(*args, **kwargs)
add_related_field_wrapper(self, 'offer')
add_related_field_wrapper(self, 'package')
Django ModelChoiceField has no plus button