I'm not sure this will work, but it's worth a try...

Instead of sending a call directly to the auto attendant, use a trunk access number as a destination, program that trunk to have a different ring tone, then send that trunk DIL to the auto attendant. May have the desired effect, although you probably won't have many choices for ring tones. Using a trunk access as a destination will make the system behave as though the call came in on a POTS trunk.

Sometimes the thoughts in my head get so bored, they go for a stroll through my mouth. This is rarely a good thing.