views.py

    def get_context_data(self, **kwargs):
        context = super(ServiceDetail, self).get_context_data(**kwargs)
        extra_fields = self.object.service_type.required_inputs()
        form = ServiceForm(instance=self.object, extra_fields=extra_fields)

        for field in extra_fields:
            input_value = ServiceInput.objects.get(service=self.object, key=field).value
            form.fields['custom_%s' % field].initial = input_value

        context['form'] = form

        return context