I see this request has already been posted, once with no reply, once with a dirty work-around (that's difficult to follow). This seems to be a straightforward addition where you can update a record if it exists, or insert one if it doesn't. The logic is there individually, but not put together. And there's no way for the user to do this, since it's hard-coded into the interface. I would imagine it wouldn't be too difficult to implement, but opens up a lot of new opportunities for Object links and extensions.