"LLC will report the vehicle use at 100% use; client should then use another "personal" vehicle for S-Corp business and get reimbursed via accountable plan.

Does this sound better?"

Not really. You report based on reality, not, "Let's just call that 100% LLC." You stated Factually this is a mixed use vehicle. Mixed Use = the amounts for the S Corps are Personal use and there is not 100% LLC. You seem to be trying to report that the Difference between the three businesses makes LLC 100%, but that isn't what you have.

S Corp 1 perspective = Employee used Personal Vehicle.

S Corp 2 perspective = Employee used Personal Vehicle.

LLC Perspective = there is Some Use of the mixed use vehicle that applies to the LLC, and it obviously isn't 100%. You told us there are the other two Uses.