Alan would know; I'll venture an opinion since I don't know for certain and that opinion is yes, it's the only call. If both the primary and fill-in driver cannot compete for whatever reason, the operation cannot use a second fill-in unless they simply want a butt in the seat and the car out on the track. Points would only be awarded to that driver, not Force. I don't see that happening.
My guess and hope is that Beckman will be fine for the next race and back in the car. And with a 147 point lead and 2 races left, Austin Prock has pretty much locked up the Championship anyway barring something really crazy.