The 2-button setup is probably the way to go, especially if you're running just 1 boomkin in the team.
Personally I'm not very fond of having multiple keys to use for a single rotation, so lately I've been messing around with menus on top of power auras to track and handle individual procs and I got to say that it's a viable option as well. Here's an example I setup with some DKs and the Rime proc:
https://www.youtube.com/watch?v=48Yi-r7WSCQ You could do something similar, where you virtualize the Wrath/Starfire mapped key in and out of the rotation for a set period of time, or until you press a menu button to swap back again. Granted this requires the click, which can be a pain to handle in the middle of a hectic fight. Down to preference I suppose.