Don't take this as gospel - I'm at work and cannot verify right now - but can't you set up Keyclone's Maximizer with PiP and just not set the "always on top" option? That should allow the second WoW region to fall to the background when you have focus on the first WoW region (or vice versa when you switch PiP).

Alternatively, you can explore other layouts whereby both WoW regions are visible and still use PiP to switch to the bigger, main region.