I suppose you could stress to them that you feel the problems are under part and full throttle, that maybe the fuel pump isn't putting out the volume consistently that it should. It is definitely a gamble, but I'd rather pay the $100 diagnostic fee and have them check out the fuel system thoroughly if nothing else. You would want fuel pressure, fuel volume, and injector leakdown tests done, basically all the diags they can do without removing components from the car. As I understand it, dealerships have the equipment to simulate real-world conditions without having to roadtest, assuming they have qualified personnel to use said equipment.