This is one reason we built Kahlua his "playhouse" (
http://www.yorkietalk.com/forums/showthread.php?t=23674) . It also functions as a staircase so he can get on and off the bed as he pleases in the middle of the night and go pee on his pad. Before we built it, he would just bark to try and wake us up, if he couldn't he would just pee on the bed. He hasn't had a problem since.