Here is an excerpt from Quint’s set report..
What’s Frodo doing in The Hobbit? I don’t want to spoil too much, but I can say that Frodo is part of the connecting tissue between The Hobbit and Fellowship of the Ring.
In fact, the next shot was an over the shoulder on Elijah Wood hammering a sign up on Bag End’s front gate: “No Admittance Except On Party Business.” You guys should have an idea where that puts this moment in the timeline.
Martin Freeman stood in for Ian Holm, who shot all of his scenes and close-ups in London. They would sometimes play footage they’ve already shot to remind themselves of what they had done previously and to help them match up shots. Peter and crew did that for these reverse shots on Elijah and I got to see Ian as Bilbo once again. It was quite extraordinary, actually. Seeing Ian in close up, wearing the wig, the vest and the pointy ears just put a smile on my face.