You'd have to distinguish one lock retical from the other... different colors maybe. You also could somehow have the primary lock resolve the targeted object, and the secondary lock target whatever it feels like? In modern combat aircraft, you either have a radar officer co coordinate multi-locking, or a good ranged radar system. Plus you only have about 6 shots of decent homing munitions. So you'd take a lot of time to resolve the lock (could be done from outside weapons range, and transfered to the missile guidance before launch) or have a dedicated weapons officer, but in any case multi-targeting while dogfighting is not something that is easy to do. If it were to be implimented in FS2 you'd have to make a secondary target display as well as raising numerous other difficulties. Being able to shoot non-aspect seakers without breaking the aspect lock would be a useful feature though I think, if heatseakers didn't automatically home in on your target if it is in you field of view.