In short, if you are going to buy the car any tax lawyer or accountant will ask you to make the payment from your own account.
Using anyones elses account doesnt have much legal worth with FBR, as such it will be a Proxy Payment.
But if you have no other option, then I cant say much, you can transfer using online banking and some people use cash (not safe or recognized by FBR for higher amounts).
wassalaam