I just leased a loaner 330i and rolled $3600 negative in: Signed: 2019 BMW 330i Loaner.
When I negotiated that deal, I negotiated
the selling price and money factor on it first. I knew how negative I was, so I knew how it would affect the payment and where I needed to be on it before rolling the negative in.
Approaching it this way also allowed me to negotiate how much they gave me for the trade-in separately also.