Call customer service and you can probably get a manager to over-ride it and push your upgrade date forward.
Back when I worked at a VZW call center earlier this year, we did this all the time. At least in tech support, we had to upgrade at least 5 customers a month. However, at that time, we weren't able to push foward upgrades for iPhones due to the very high demand for it. It may be true for some of their newer, popular devices as well. There's always a catch...
Managers would be more than happy to push forward an upgrade date by 1 month at maximum to make a sale happen. We even had competitions to see which employee had the most upgrades and also which team comprised of 10 employees each in the whole call-center had the most overall and would get rewards for it.
Go for it!