Or simply use our ReelSmart Mtion Blur that tracks the moving parts of an image and applies blur in the calculated direction and amount that each pixel is moving (if no movement is calculated, no blur).
Demo version located in the Downloads subsection for RSMB on our website:
http://www.revisionfx.com/products/rsmb/
The $89.95 version of the plugin unlocks the "regular" plugin, which will perform the blur based on calculated motion. Note: there are 2 plugins in the Pro version that provide more features, and is prices at $149.95... but I don't believe you need that for what you are describing.
Pete Litwinowicz
http://www.revisionfx.com
