In practice Jetblue really won't let you use certificates on corporate bookings? By comparison Delta will take over reservations to process RUC/GUC.
The variable upgrade cost is a little concerning, hopefully 4 certs will still be enough for at least one LAX-JFK round-trip in Mint on most flights. A cut in half of value would be worthwhile if they can be confirmed in advance. 3x cost would be less favorable.