> //2.  Works and looks clean but has the iterator range as part of the call.
> std::for_each(tokens.begin(), tokens.end(),
> phx::push_back(phx::ref(string_tokens), phx::arg_names::arg1));

Using the Boost.Range library, that would be:

boost::for_each(tokens, phx::push_back(phx::ref(string_tokens), phx::arg_names::arg1));

I think that's about as clean as you can get.