I've been doing this forever.

All of my spells are prefixed with:

/target [target=focustarget,harm,nodead][target=party1target,harm,nodead]




You should've seen me on IRC trying to explain this to Xzin. :P

My "switch main" buttons are:
/promote <newMain>
/focus <newMain>


If I'm in a BG and I know I need to keep my focus, I don't use complex CC. If I'm in PvE I can feel free to reassign my focus after my "switch main" button and not lose my normal functionality since the main has been /promote'd.