'fixed' covariates in nlmer

Dear Laurent,

Did you ever get a reply about your message below?

I am also investigating the same problem.  
My impression is that nlmeR  (lme4) is currently intended 
just for the individual fixed effect estimates and that the population 
values you describe would need 
to be added in the random effects.  
So I think that if for some reason you need these in fixed effects 
rather than random  then we would need to use nlme.  
Is that also your impression and what you 
ended up doing?

Many thanks

Cheers
Chris