Yeah, I have little patience, so if I can't find it easily, I'll just reach in and pull out a good portion of the inside! I'll just pull out a bunch, whatever comes out easily, and innevitably I'll see that there's only one strand connecting this portion to the rest of the ball: so I know the end is in there somewhere!
If I can't spot it easily, I'll just start unwinding it from the part that's connected to the ball, until I reach the end. Then I'll wind it back up starting from the end I've found, just wrapping it around and around my hand, and holding the end with my thumb so it doesn't get burried and lost. Then I just stuff that wrapped up yarn back inside the original skein, and I'm all set to use it as a center pull ball. It sounds like a pain, but it doesn't take that long, and it eliminates the frustration of searching and searching forever for that end!