[Rcpp-devel] Using Rcpp in a package only as an option?

Hello dear list members,

Following previous correspondence, I wish to use an Rcpp function inside
a package I'm authoring.
However, I do not wish to force the user to install Rcpp, and if he does
not wish to do so, I want to let him "fall back" on an R written
function (which is 20-40 times slower, but it works).
Looking at this Vignettes:
http://cran.rstudio.com/web/packages/Rcpp/vignettes/Rcpp-package.pdf
I see that including Rcpp in a package require the use of "depends" in
DESCRIPTION.
Is there a way to have Rcpp as "Suggests", and to later use "require"
when loading the package, to decide if to load the Rcpp function or the
R function?
(alternatively, I could have a separate package only for that function,
but that feels a bit like a "hack" to me)

Thoughts?

With regards,
Tal