Yeah, that would be wierd anyway, going from one therapist to a different group in the same day, or the same time period for that matter unless you were switching.
I would say there must be an explanation as to why the patient saw two therapists in the same day. I would send in a written appeal (if the auth would cover both visits) explaining the reason the patient needed to be seen. It's really the only option. I'm not aware of any other way to indicate it. Even if you use the 77 modifier, they will want to know the circumstances, they most likely wouldn't just allow with the 77 modifier.
Michele