Ragdolls and helper bones?

I have some helper bones which are driven by bone constraints (copy rotation) in the 3d modeler. But it occurred to me that these are not going to work when the character is changed to a rag doll. So the question is – Is there a way to duplicate the functionality of a constraint in rag dolls? What I need to make this work is to have the helper bones copy the rotation of the source bone with each animation tick. Otherwise, the player model is going to look pretty weird.