Hi JC,

The original Gompertz function is called SGompertz in Origin's NLFit tool, 
and can be referred as nlf_SGompertz(x, a, xc, k) in your user-defined 
fit function. Say, the original function is called G(x), and your modified 
function is Gm(x)=am*exp(-exp(k*(xc-x))); Then, 
  Gm(x)=G(x)^e , and am = a^e

Therefore, you can define your function Gm as:
 nlf_SGompertz(x, a, xc, k)^e  .

You can also define a derived parameter am such that 
 am = a^e

Hope I didn't make mistakes; (sorry if there...)

--Hideo Fujii
OriginLab