I'm slowly getting all the lights turned out and a bushel of little things repaired on my "new" xk8. the cup holder was near the bottom of my list so I've had time to search for how others had repaired the broken hinge. I didn't see this method, but it worked really well for me, so I figured it was time to pay some back and share it.
Wile digging through my bin of odds and ends, in search of anything that would help me repair the broken "eye" I came across this little clip that's normally used to attach phone line on the outside wall of your house. any home improvement store should have them. I tossed the nail and drilling the hole to 1/8" so a very small screw could be used to secure it. the broken area was cleaned up and ground square to accept the new piece, and a small guide hole drilled to accept the threaded portion of the screw without splitting the plastic.
In my case the pin on the door was also broken, as well as the bail that stops the holder at the right position, I used a piece of inner boden wire to fabricate the bail, and JB welded in a new (metal) pin. but nothing special about repairing either one of those things.
One of the "stock" clips is also shown in the photo so you can see what it started out looking like. they are a nylon type material and quite strong, so that should last a wile.

Cheers,
Russ