I need a survey application very soon. django-survey seems to be nearly what I am looking for. But one feature is missing: conditional questions

i.e.:

> 
> have you been taking part in this....
> 
> 
> yes no
> 
> 
> if your answer is yes, please proceed
>  with Question 1.1. if it is no, please
>  proceed with Question 1.2
> 
> 
> 

Here it should be checked, that 

> 
> if yes -> 1.1 is answered and 1.2 not
> 
> 
> if no -> 1.2 is answered and 1.1 not
> 
> 
> 

Do you know a way to implement a conditional-check hack for django-survey?