I wouldn't patch/change the EsbActionHandler in this case, because it leads to a design trap in my eyes:
You start to hand in variables from jBPM to the DefaultBodyLocationMap with the keys you need in one special service (e.g. calling a WebService, so you will have "sayHello.toWhom" and stuff like that as variables).
A cleaner approach is really to use Smooks (I think it should work even this way, but I would have to look at it) or maybe an own ESB-Action, which gets together all objects into a Map or maybe is configurable to create the correct map.
Does this sound logical?