Yeah, I think I agree with you. Usually with Carrey he goes so over the top and isn't quite believable, even while being very funny; but here he managed to submerge his desire to be noticed and played it so straight (and for the entire ceremony, not just when he was on stage) that no one really recognized him, even his friends.
The costuming was also great -- his height of course isn't maskable, and if you know it's him you can recognize his actual face, but the hair and the extra padding in his costume really change his body shape so it doesn't resemble him. And he had the speech and mannerisms so effectively that it comes off believable versus a pure caricature.
"Hey Capa -- We're only stardust." ~ "Sunshine"
“Pleasure to me is wonder—the unexplored, the unexpected, the thing that is hidden and the changeless thing that lurks behind superficial mutability. To trace the remote in the immediate; the eternal in the ephemeral; the past in the present; the infinite in the finite; these are to me the springs of delight and beauty.” ~ H.P. Lovecraft