Using "optim" function in R for making profile likelihood for a parameter

Question

I am using the maximum likelihood method to estimate a set of parameters. Particularly, I use "optim" function in R to do the optimization task. Now, I am going to make the profile likelihood for each of the parameters. I wanted to know how I can do it using optim function? Is it possible to force optim function to keep one of the parameters fixed during the optimization task?

here is part of my code that is supposed to do the profile likelihood for "lambda" parameter. Here box is a boundary around the maximum likelihood.:

profile_design(
  lambda=seq(0.003,0.008,length=40),
  lower=box[1,c("gamma","alpha","beta","p0")],
  upper=box[2,c("gamma","alpha","beta","p0")],
  nprof=15, type="runif"
) -> guesses

registerDoParallel(cores=600)
registerDoRNG(123456)
foreach(guess=iter(guesses,"row"),.combine=rbind) %dopar% {
  out <- optim(unlist(guess),ml,method="Nelder-Mead",
               control=list(trace=4),data=dat)
} -> pf

But using this code, "lambda" parameter would be changed during the optimization task, while I need it to be fixed for making the profile likelihood.

Thanks!