Going to be extremely difficult to reproduce the same qualities. Overmolds are often chemically interlocked and mechanically interlocked. Essentially making the two inseparable. Its also the most economical way to get soft gripability and the strength of the main plastic body in large volumes. Trying to recreate that while also maintaining the design is pretty damn hard short of having a bunch of tight fitting orings wrapped around the grip. Might work but doubt would fit your design vision. Instead of trying to duplicate the process try exploring the materials. Maybe there are some bio friendly soft and hard compatible materials.