How do you fish a spinnerbait on a drop off that goes from say, 8ft to 22ft?

Um, very slowly?  LOL   ;D

There is a new spinnerbait on the market, by Strike King, called the Rocket Shad.  These spinnerbaits are created just for this purpose.

However, if you don't have any of these, and are able to change out the blades, I go with a 1/2 head, with 2 willow blades.  The front one around 4.5 and the back at either a 2.5 or 3.5.

One technique that you can try is to yo-yo it up or down the ledge.  This gives the impression of a dying shad, which is a great way to trick bass into feeding.

I suggest using a slow reel, 5.2:1 or 5.3:1, depending on what reel you are using.  This will force you to slow your presentation down.