Okay, this way is easy enough -- I assume you are just exporting the head and working on the eyes? 

You don't need to move the eyelashes with a magnet -- just create a new group using the eyelash material as suggested by Miss Nancy.  Export the head as morph target, including groups. Resize to prevent rounding errors if you're using 3.1, using either the free objaction scaler or the poser scaler plug-in.

Import into zBrush, and ctrl+shift click the head. Since the lashes are now a separate group, they will be hidden.  Do your morph, then ctrl+shift click on the canvas to show all the mesh. Your eyelashes will reappear. With your head and eyelashes visible, you can now export, resize, and use as a morph target.