[Elladan and Elrohir]

Well, for me this one is easy. No.
For all the grousing about Jackson's propensity for CG, I think he would have done a live-performance Gollum if he thought it were at all workable. Do we get how much money had to be spent bringing a CG Gollum to life?
Part of the whole point about Gollum, at least from my point of view, is that a good deal of him is no longer human (or hobbit, whatever). I don't just mean psychologically, I mean in his appearance.
I think the filmmakers struck the perfect balance: an animated Gollum that relied heavily on Andy Serkis, not merely for voice and visual reference, but for facial expression and body language. It's easy to watch the film and see that Gollum is part human in the sense that he was a fairly normal person before possessing the Ring. And I think it accomplishes that in a way that no human actor in the world could do on his own.

I of course greatly respect alatar and others who adore Peter Woodthorpe's performance as Gollum in the BBC radio version, but I found it one of the most unsufferable pieces of the entire whole. Everytime he spoke, I cringed and wondered, "Is this the most Gollum-sounding anyone can be?" I think I prefer Tolkien's Gollum to Woodthorpe's, and Tolkien wasn't acting, merely reading.
Serkis' Gollum-voice, to me, will always be THE Gollum; like his appearance, it simply doesn't seem very human -- and in this case, the credit goes exclusively to Serkis' unenhanced performance.