When train cars get together, they form a coupling that is kind of like a handshake, where the couplers (I think they are called) join together, and one pulls the other along with it. When they want to decouple the cars, they stop grasping each other and go to a sort-of extended fingers position.
What if you were to have a special collision blocking volume a certain distance from one actor, and it only blocks a specific volume and the actor. Then you could probably put another of the same type of collision blocking volume on another actor that is also a certain distance from it. Now if you placed one blocking volume within the space between the other volume and its actor, theoretically it should pull along that other volume, the actor coming with it.
Then again, it’s probably just a crazy idea I just had, daydreaming about trains while I am at work…