It astounds me that through my research and own trial and error, I've yet to find a way to add a boarder to a standard, left-right wipe. Is this really the case? I'd be doing this for a series of different shots, a reel being made using mixed formatting so going to a standard NLE is not in my best time interests.
After working with Action and using some great tools, I'm surprised that Smoke wouldn't be my friend on a much easier task. Hopefully, it is.
it's not large at all, just colored frames with the aforementioned wipe setup. Render it and you can see there is a line where i've edited the top-layer wipe.
If you want more eye candy on it, like a drop shadow or anything like that, you can make a ConnectFX gap effect over the wipe and go to town. Simply copy the axis within the lower wipe and paste its animation into any axis in your ConnectFX, and parent anything to it within an Action or 2D Transform node.