In 2D mode, Unity auto-scales so that the height is preserved (you don't have a say about it), and it clips by width to fit the aspect ratio.
I'd second your friend - start with a high resolution and a specific aspect ratio. Later on, you can hide certain elements, or move other elements you need to be at the edge. I've found that programming in Unity for different aspect ratios is not such a pain in the ass. I expected a lot worse :)
To make this work, create a big background - bigger than any resolution you'd normally support. Put at (0,0,0) - so that it is always centered. Make objects children of each other. Create a script that will position its GameObject at the proper edge (top|bottom, left|right) with random offset (x,y) when the scene is initialized (Start). You can use the main camera's aspect ratio (Camera.main.aspect) to determine the proper coordinates. Have in mind that origin in Unity is by default (0.5, 0.5) and that it uses Cartesian coordinates instead of the typical (0,0) for top-left corner of screen. Also, the default mapping is 100pixels=1 unit. Don't forget to set-up your orthographic camera for your default resolution (it's size is your default resolution's height / 200).
We use this and additional tricks to move objects proportionally (up to a point) for a second project, and it works quite well so far. The cool thing is that you can test it in the editor itself. The only problem with this approach (dynamic location by x based on aspect ratio) is that you need to run the game to see objects in their real position.