Hello,
From my knowledge this isn't possible. It is likely that the mane "presets" you saw, were actually a re-textured mane as a modification of the game, or they included their vanilla design in the preset, which is possible. If you can find the google images you were referring to, that might help. I tried a few things in the code and couldn't get it to work. It seems as though you need body textures, and the rest of the textures in order to get it to work properly. I will do a little bit more research, and if I find anything I will let you know. But, as for now, I don't think there is a solution, or I haven't found one as of yet.