I have heard stories about this being possible in the past. However as the KL service center does not even wanna handle irrops for Expedia-booked tickets, I think this might be difficult.

During check-in you can link your itineraries, at least for that BP. Your guest will be able to also choose a seat in the preferred seating area, if you are lucky even the exit row might be available for free. I have also seen your FB level being printed on the guest's boarding pass, making it very easy to use the express security lanes and so on. Nothing of this is guaranteed though as it seems to differ per destination (Strange but yeah)..