There's a kicking system where you place your cue perpendicular to the nearest rail with your tip at the center of the ghost ball of where you want to hit. Then pull your cue back to measure twice the distance from the rail to the center of the ghost ball and it gives you an imaginary point to aim at. It's hard to explain in words but I know a lot of players use it, especially when kicking or trying to make balls going rail-first.
Maybe someone can explain it better or provide a link.
Here's a video of Chris Melling using it to shoot a kick shot in a match (around the 1:20 mark)):
http://youtu.be/iO_aJYcG4f8