Softbody Collision Callback

[GLPhysx]

Is there anyway to setup collision callback on softbody?

Im using:

psb->setCollisionFlags( psb->getCollisionFlags() & ~btCollisionObject::CF_CUSTOM_MATERIAL_CALLBACK );

and register:

gContactAddedCallback = gameCollisionCallback;

But the function never get called for my softbody, am I missing something?