If you use dhenry's approach be prepared for a lot of typing:
case (KEY_A | KEY_B): //then something else
case (KEY_A | KEY_C): //then something else
case (KEY_A | KEY_D): //blah
case (KEY_A | KEY_E): //blah
case (KEY_A | KEY_F): //blah
case (KEY_A | KEY_B | KEY_C): //blah
case (KEY_A | KEY_C | KEY_D): //blah
case (KEY_A | KEY_D | KEY_E): //blah
case (KEY_A | KEY_E | KEY_F): //blah
case (KEY_A | KEY_F | KEY_G): //blah
And so on. It doesn't lend itself to this situation.