Shape Keying Eyelashes with Eyelids?

So what if I have mesh-based eyelashes that I would like to apply the same blinking shape key to. What would you say is the best/easiest way to do this? Having both eyelid and eyelash in one object, or make both separate objects and apply separate shape keys? I ask because sometimes when I tell blender to mirror the shape key, it doesn’t do it to the eyelash, or if it does it isn’t deforming right.