The corners are a fantastic trigger. Unfortunately, the “Hot Corners” option in Prefreneces is constrained to a handful of predefined actions. Enter CornerClick which allows you to take total control over your corners. The developer opensourced it in 2010, and it doesn’t look like any development has occured since then. That said, I am using it in Yosemite and it is working for me. I set the trigger to Hover which works well.

Set actions for each corner, modify the trigger with hot keys, hover, click, etc. There a handful of predefined actions (including “Desktop” and “Screensaver” that I used with Hot Corners). In addition, there is an ApplesScript action which opens the door to trigger just about anything you can dream up.

I hope someone with inclination/spare time comes along and updates this. In addition to the corners, being able to define an active area on the side of the screen would offer additional trigger points.