Photoshop effects: selectively apply special effects to one side of an object

Add special effects to sides or parts of element individually. Periodically, when I create CSS sprites, I sometimes need to apply apply partial effects.

For example: add stroke to left side only. or two sides: bottom and right.

Or what about drop shadow that only appears on the left side and even if the spread is very wide, it doesn't peak out of the top, right and bottom.

I guess this mainly applies to effects that appear along the edges: stroke, outer glow, drop shadow, outer shadow

It gets hard if PS has to keep track of the number "sides". I guess it's easy if the object is square.

Unless there is some way to "manually paint" the special effect onto the object with some sort of special "effects paint brush" such as the image below

http://www.flickr.com/photos/31792685...