Is there a way in the Coot GUI that I can build two helix of the same sequence (or just short 5aa or 6aa peptide chains of the same sequence) that run in the opposite direction (180 degree opposite direction) of each other and set half occupancy of each peptide chain?  

I tried to use Calculate---> Model/fit/refine/----> add alternative conformation, but it seems I only have two options: "split single residue at C-alpha" or "split all of a single residue", which are applying to single residue only, not a short peptide chain.

Thanks.