Are you looking for a 3D ray cast query? Did you try using the rayTest query using the dynamics world?
virtual void rayTest(const btVector3& rayFromWorld, const btVector3& rayToWorld, RayResultCallback& resultCallback) const;
"I looked myself into the code of bullet demos, and what I understood is that there is a raycast from the camera to the 2D screen, testing the collision of the casted ray with the objects of the scene. this technique will not work if you must do a raycast from a 3D cursor in your world though."
The ray cast query in Bullet is generally in 3D, with a 'from' and 'to. Why would this not work?