When you say Andrew Kramer's tut do you mean this one, using Lens Blur referencing a Depth Matte (solid with Ramp)?
http://www.videocopilot.net/tutorial/2d_depth_of_field/
If you have AE 7 or above that should do nicely, or if older you could use masks on duplicate layers and blur the lower layer, but seems that would be more tedious, no?