I don't understand. Are you trying to advise a client not to use a vehicle they just bought except for some limited functions, only? And you think there is a tax regulation that makes this advantageous?

"It appears having new vehicle be a mixed used vehicle would not yield the best results."

You do what matches the Reality.

Why would someone buy a new Truck and then let it sit around and not be used, when that is why they bought that vehicle?