So a P2P mixture of amphetamine is in DCM.  Yes one could use 20% HCl in water to wash the DCM with to removed the amphetamine but the concern is that the amphetamine wont "see" the protons since the HCl/water and DCM are not soluble.  Maybe just shaking the hell out of the DCM/HCl/Water mixture will be give the amphetamine sufficient exposure to the protons?

Yes, that's how you generally perform A/B workup. Shake the hell out of that baby, and you'll have your material in the water phase!