The numbers I picked out were just examples (random). Also, legally they would not be able to "include" the 7500 in the lease up front since it is technically not a guaranteed thing. Volvo Financial needs to have tax liabilities in excess of every 7500 they claim, or they won't get it. And yes, it is all a bet on future value and all that (and was never implying it was an open ended lease, but lease offers change every month, including residual values.)
What I am saying is, when they set the lease terms, they look at the various projections and set them based upon the information they have including their projection for recouping the 7500. If they didn't factor that in in some way, the lease would likely be much higher. And some of that may be put in to that lower residual value as well. If you are someone who never plans to buy a lease, the best lease is a low money factor, high residual. Your payment is low, but you'd be crazy to buy the car at the end. But a Low MF, Low Res gives the buyer options.
If there was a way for them to truly show the 7500 (or in your case, 3750 with a 50% residual) in the paperwork, they would. Heck, that's one of the primary complaints people about the rebate is that it is something they still have to pay for out of pocket. At the end of the day, I crunched the numbers when we were looking at our P8 and the lease cost slightly more in total than purchasing it outright. But it was close enough to be negligible if we had been in less of a rush at the time. I don't remember the exact numbers, but I feel like the lease time period would have been lower (with no money down) but then the final two years of financing it would have been higher than the single financing term, while the financing was constant (starting higher, but then either having the 7500 applied after next years taxes).
If you have your contract handy, it should be pretty easy to figure it out. Get the total of your payments and any down you put, total that up. Take your residual, plug that into a payment calculator, add sales tax and calculate at about 3% interest for 24 months and add those together. Then take the "price" you negotiated, add your local sales tax and any fees you know of (e.g. doc fees) and plug that into a payment calculator at around 2% for 60 months (or pick a promo if they have any going right now). Get the total of those payments, then subtract the 7500 (yes, you can refinance once you get the 7500, but that's more complicated and nuanced). I'd imagine the lease will definitely cost more using that method, but it isn't going to be 5000 more. Maybe 1000. But that's the price of flexibility (it is also very rare that a lease into a purchase is the cheapest way to buy a car. It does happen, but not often).