applescript to choose Finder's "remove from dock" Dock context menu option, if present -- assumes(?) that this option is the 9th line in the context menu. also it temporarily mutes the system volume so you don't hear the "poof" sound effect.

gistfile1.applescript

tell application "Dock"
        activate
end tell
try
	set oldvalue to output muted of (get volume settings)
	set volume output muted 1
	tell application "System Events"
		tell process "Dock"
			set frontmost to true
			activate
			tell list 1
				perform action "AXShowMenu" of UI element "Finder"
				delay 0.25
				repeat 9 times -- count number of items to the one you want
					key code 125 -- down arrow
				end repeat
				delay 0.25
				repeat 1 times
					key code 36 -- return key
				end repeat
			end tell
		end tell
	end tell
	
	
on error
	
end try
delay 2
set volume output muted oldvalue