the closest thing may be to use the native 2D dock, and edit the files for the border here:
/System/Library/CoreServices/Dock.app (right click show package contents)
like bottom1.png to bottom5.png
(or right1.png to right5.png, if you use your dock on the right.)
Those are the image files that outline the 2D dock.
Make them transparent and the 2D dock will be "borderless," (but still have the translucent-gray background).