Can you set a focus target on PS3? that's how I target all my bosses as the tank. Set focus, then when I got to round up any adds and see that the boss is casting something that I need to interrupt I just hit the 'target focus target' button and wham I'm back on the boss no matter if they're even on my screen.
You can also macro target's target to target the tanks target, or mark the target and target the mark