Epoxies are thermosets and generally very solvent resistant. The best you're going to do is swell/soften the epoxy so that it can be mechanically removed more easily. But most of the solvents which work with nearly-cured epoxies (i.e. to clean paint guns using epoxy coatings) will swell NBR significantly and may lead to damage of your NBR parts- depending on what exactly they are.
Ethyl acetate is one possibility. At room temperature, NBR (BUNA) seems to be relatively resistant to this one, but most of the epoxies indicate "not recommended" at any temperature. It's also a component in the paint gun cleaner we use with epoxy here. The co-solvent used in that mix (xylene) wouldn't be such a good choice due to the potential to swell your NBR part.
What about sandblasting? NBR is incredibly wear resistant, whereas the epoxies aren't nearly so. Depends on the intended use and geometry of your part as to whether or not this is a good option.