Your method is interesting neil, I'll have to try it. I aim more or less as cuetable diagrammed... double the distance method. Here's a more exact breakdown...
1. double the distance from the 2nd OB to the rail and imagine the ghost ball on the opposite side of the cushion
2. Aim ball 1 to hit directly into that ghost ball. This won't sink the ball, rather it would hit the ball in the face.
3. Now adjust to cut ball 1 even more. You cut it more by the same amount as you'd need if you were to cut ball 1 into ball 2 directly. So if it's a half ball hit to sink the 1 with the 10, you now aim to cut half a ball further than your original line.
4. Try hard to visualize the back of the first OB as it contacts the rail, once you've staked out a spot on the rail. Does this contact point just with common sense? Can you visualize it going down this way? Sometimes this common sense check reveals I'm over or undercutting a bit and I repeat the previous steps to be sure I haven't screwed something up.
5. Account very slightly for the fact that the first ball is going to come off the rail a little wider than expected (due to collision induced spin or just general rail effects from a gently used rail). Most of the time I find I need to cut the ball even a bit more to compensate for this.
6. Fire away, aiming at that spot on the rail that you picked out as if it were the center of the pocket on a shot you really wanted to drill in dead center. Use a nice medium speed, as funny stuff can happen if you hit this too slowly.