alternatives to do.call() when namespace is attached but not loaded?

Dear R-devel

I have a function in a package that essentially provides a wrapper for a
group of functions in another Suggested package (it sets appropriate
defaults for the context, transforms output, etc).  I've implemented this
by verifying that the package was loaded with

require(sna)

and then

do.call(snaFunName, args = args)


The rDevel check is requesting that I use  requireNamespace(sna) instead
of directly loading the SNA package. This seems reasonable, except that I
have yet to figure out a way to use do.call to call the function when the
namespace is attached but package is not loaded. do.call("sna::funName",..)
doesn't seem to work.

1) Can do.call() call functions that are only namespace attached? Is there
better way to accomplish this without do.call()? For example, should I use
getAnywhere('funName') ('tho this doesn't seem to permit restricting search
to a specific namespace..)

2) Is this an appropriate of require() instead of requireNamespace() to
ensure that the Suggested package is loaded and attached? Can I ignore the
check warning?

best,
 -skye