You should be able to sign up for verizon device payment plan at the apple store once your upgrade is cancelled. (I signed up for my 6s+ at the apple store under verizon device payment and no credit check was done since I was already a Verizon customer). What I'm not sure about is if its something that happens instant or takes a few hours. I would check with Verizon. I would go ahead and reserve if it's still available and then check with Verizon on canceling/reversing the upgrade.
I currently have a 256 JB + on order from Verizon, but just reserved a 256 MB + at the Apple store. I'm probably paying full price for the phone at this time. My JB is set to arrive on 9/28 (if that happens, saw someones got backordered from 9/28 to November...). If the JB actually comes in, great, I can just return the MB since I'll be within 14 days. If not, I will be cancelling the JB and keeping my 2nd choice which is the MB.
It's a shame we have to resort to things like this because of a botched launch like this one has been. Good luck to everyone!