Both modeling human body response to dynamic loading events and developing biofidelic human surrogate systems require accurate material property characterization over a range of loading rates for the various tissues that constitute the human body. This work describes a technique for measuring the shear properties of soft biomaterials at high rates of strain (100 to 1000 s^-1) using a modified split-Hopkinson pressure bar (SHPB) technique. Establishing a uniform state of stress in the sample is critical for high rate testing of this type. The technique presented includes direct experimental verification of the uniformity of the stress in the sample using piezoelectric quartz force gages on both the input and output sides of the shear specimen. Maintaining a uniform stress within the specimen from the start of the test requires input pulse shaping to ramp the incident loading pulse. Soft foam pulse shapers are used to control the loading when testing the response of compliant biomaterials that are subjected to peak applied loads of only ~3 N. Preliminary results from fresh and frozen porcine brain tissues and silicone-based biosimulant materials are presented. Future experiments will utilize the technique developed here to characterize both human biological tissue and candidate biosimulant materials and compare their dynamic mechanical properties.