[Ifeffit] Fitting bond lengths without a known FEFF file

Dear list experts, Here is another challenging question for me; can someone help? I have soil samples, trying to fit the first shell, I have 3 different optional bond lengths, which might give a lot of information. Now I have two questions: 1. If I do not know of specific structure (XRD implies a very amorphous material), so no specific FEFF file that I can use. what would be my way to determine the parameters for IFEFFIT (Deg, Reff, amp,...)? 2. Is there any option to fit the 3 bond lengths together (no dependency that I can think of...)? Should I fit all pairs, then accordingly assume one component; 'set' it and fit the other two as fractions of 1 (N+(1-N)? Thanks!!