I know what you mean, building some angled mounts like that was my second option, and really the only way to do it if you have a flat wall. It really would not be hard to do though, you would just have to make sure you didn't make the fatter (outside) part of the bracket so thick that you could no longer pinch it and the drywall with the speaker bracket. I guess you could always get longer screws for the speaker bracket if you had to.
(If you don't actually have the W's in hand this may not make sense, but once you see the bracket, it does).
