I've started using HotKeyNet.

I edited the script so that it would launch 5 instances of wow and resize and position the windows, it'll take a some fiddling to right, if only there was a way to get the position and size of all the windows on screen.

It seems I've found just what I was looking for. I'd come across the HotKeyNet site in the past, but didn't look any deeper since I had assumed that it was used only for broadcasting key presses to multiple applications. It seems to be quite flexible and well maintained.