[New2rt]

I've done this many times. Go with the owner when it's paid off, you can make the payment direct to BMW financing and give the seller the difference between payoff and selling price.
BMW will have the title and they will send it directly to you with the proper documentaion.
Just be sure you are present when this happens.
I wouldn't send the money and wait for the owner to send you the title (the title should never go to the seller, sent direct to you) I was almost bit by this once, almost.

If you are also financing, your bank will handle the transaction with BMW financing.

 

[New2rt]

You need the owner's signature on the title to indicate transfer to you. In some states, you also need an additional form (in Texas it is Title Application and odometer statement) signed by the seller.

As for registration, you would likely need to register it in the state where you live, which may have to wait until you get home to do, if you live in a different state than the seller.

Some states (Texas included) offer 15 and/or 30 day tags, allowing you to register the vehicle in that state for a short period.

When buying a bike out of state, I have not bothered with the temporary tag. I either use the existing tag to get me home, and I might consider going with no tag with a bill of sale and title in hand. My state allows up to twenty days (last time I checked) to get the vehicle transferred into my name.

Hope this helps.

I don't know about all states but in PA they use an e-title untill it's paid off, then you get a paper title.
Of the last 4 bikes I bought, sold, or traded I never saw the title.