Always a tough leave, and about the only way to cover it is to throw a missile and hope for a bounce. At one of the houses that I bowl in, there's a cover piece missing from the pit.. if you throw the ball hard enough, the 10 comes out every time. lol! Needless to say this makes the pin chasers quite busy when I get on that pair.
Here's an interesting example.. Last Monday night, I left a big 4 (4-6-7-10). It was early in the game, so I went for the spare, just missed the 6, hammered the 10, watched the 10 bounce out and take out the 4. I don't think that I have EVER seen the 4-10 chopped off of the big 4. lol!