回复：How can we work out this?

First he needs to payoff his car so that he can get the title - before he pays off, he doesn't have the title at all.
Second, he gives you the car as a "gift" - put the "gift" as the price on the title. In this way, when you go to register the car, you don't need to pay any tax.
And then, you pay your BF money according to the agreement between you two.

The whole thing works if and only if you and your BF trusts each other, esp. your BF trusts you. Imagine, if your BF gives you the signed title with price of "gift" and you don't pay him? (Only a joke :-))