Since the iPhone runs a version of OS X, I would assume that there's a way to do this through terminal.app. For example, in OS X on a Mac, you can type this:
defaults write com.apple.Dock mineffect scale
in Terminal to make the effect happen faster.
There are at least 2 issues though...
#1. The iPhone must be jailbroken so you can install the terminal app
and more importantly,
#2. Where would this setting be located, if it's available to be changed at all...