Is there a way to change the amount of time you have to click and hold on a Dock icon to activate Dock Expose? or maybe tie the right click to activate it?
I'm not aware of a setting for just clicking on the icon with the mouse other than a default for turning it off...
defaults write com.apple.dock show-expose-menus -boolean
You can change the behaviour of when you drag a file onto a dock icon though...
Go to Finder Preferences and at the bottom of the general tab there is "Spring-Loaded folders and windows"
You can dis/enable it and change the delay time.