Well with a lease, depending on the terms, there would be nothing down, or he could do whatever small amount he wanted. Certainly putting down less than 4k, and as for the trade in, I would sell it and keep the money. Thats what I would do, but I wasn't telling him to do it, I just offered the idea.
I own two vehicles, and will be leasing another higher end vehicle soon. I enjoy leasing really nice vehicles because I can trade them in for a fresh one after 2 years or earlier if I like. The vehicles I own are customized and hold value well. I personally don't see the point in purchasing new (used is better) vehicles that degrade within minutes of leaving the lot. If you don't own a vehicle then I understand. If it is a classic or special edition, I understand. If it's something you absolutely cannot live without, I understand
However, once that vehicle reaches a point where your warranty is invalid and things start falling apart, most are ready to trade it in. In lower end vehicles, you can easily fix them at a low cost. When you're driving a mercedes, bmw, audi, or some other luxury car, those cost can skyrocket. They also don't hold value well, so you may be upside down when you are prepared to turn it in. Theres a lot of money and value lost in the purchase of a luxury car and IMPO, they're not worth it.
Lease a model you like, turn it in, upgrade or lease the same newly released model, rinse and repeat.
