Let's do some simple things first.

load a cube in carrara. Subdivide it a couple of times so you have a few verts to play with and export it as an .obj. make sure you saved the subdivided cube as an .obj or in your browser or as a scene. You want to use the original to add the morph to.
Import it into what ever modeling software you want to use. Move the verts around how ever you want. Export as .obj.
Now load your original back into Carrara and then load your morph to that. It should work as a normal morph with dials and all.

Also let me know what your using for modeling software. If it's Hexagon or Wings3d I can give you the Import/Export % for those two as I have posted them in those forums here and with my hex tutorial at Poserpros.