how to stopbody enabling by joint

Hi all,

I would like to join rope to a platform, so I can move platform, and 
rope will swing according to it. But I don't want rope to pull down the 
platform. Mainly I want to have similar results to results of making a 
joint between 0 and Body, but with possibility of moving this pinning 
point, and setting this pin as Ball with AMotor joint in Euler mode (so 
I need two bodies, becouse in Euler mode first axis need to be attached 
to body one, and third axis to body two - so I can't make a joint 
between 0 and body). How to achieve this?

Cheers,
Krystian