You cant.

A morph in Poser always applies to the complete bodypart.
Otherwise youll get the "Wrong number of vertices" error.
When you import a morph into Poser, it isnt for example just ears, but a complete head WITH morphed ears.
Or a complete head WITH a smaller nose. Not just a smaller nose.

You can use groups to create morphs, but you cant use them to extract "sub" morphs. (Like Faerie-ears from a Faerie head morph). Poser always saves and uses the whole bodypart as a morph.
And modellers also always export a complete bodypart as a morph.

Theoretically, you could use a text editor and only extract the deltas for those vertices that belong to the ears, and then fill the rest up with unmorphed vertices to make the vertice count correct again. But youd have to know the exact data for any vert that is part of the ears.

There is also the chance to import both your Faerie morph and an unmorphed head into a modeller, cut along the ears of both and simply switch them. That new morph would only create new ears but leave the rest of the head unmorphed.
This doesnt work in Wings3D, because it renumbers the vertices, but might work in over modelling programms.

stahlratte