Click on "General" at left of main config screen.
Click on "Miscellaneous Options" button.
At bottom of new window is "Advanced Options for Magnifying Docks" "Attention" Effect
Select Bounce.
Only standard docks can use bounce, tabbed docks won't. Don't think you actually have to have magnification turned on, but maybe.
As far as I know, there is no additional option such as "until gets focus" or such, or to adjust timing of bounce, it just bounces or it doesn't.
Happy bouncing. 