You can't without heavily modifying ACN. I mentioned some time ago that the only way you might get away with it is if they had left several abilities blank on ACN, to be determined by which carbuncle is out, and carry over into SMN and SCH depending on what they have out.
Even then, current SMN gameplay in XIV is solid, especially seeing they're great DPS and have back-up utility via battle-rez and Physic. I wouldn't throw that to the wind for any reason, really.
