First off, it sounds like you're attempting to do what our LEDBlinky integration/app already does. I'd look into that app first and see if it does what you are looking to do. I've not used it much but the end goal you described sounds exactly like what that app already does.
Secondly, the BigBoxThemeElement interface needs implemented on a custom WPF theme control that gets added into the view of the theme you are using. If the control isn't in the theme you won't hit those break points.