The AS2 is designed to fly 4,750nm at Mach 1.4 or 5,300nm at Mach 0.95. That's plenty of range for the planned mission profiles.
Flexjet is primarily a fractional-ownership company, and a big percentage of their client base are corporations (vs. individual customers). They can place these jets on coastal hubs and offer their customers supersonic transatlantic and transpacific flights -- NYC to London, Paris or even Moscow; SFO to Tokyo, etc.
For these corporations, the flights could be considered a deductible business expense. With oil prices forecasted to remain low, I'm sure they can work out the economics.
Having said that, Aerion is majority-owned by a billionaire, and I'm sure he and his buddies are looking forward to jetting around the world at supersonic speeds.