I think they should keep the characters true to the way that they were in the book.
When they blew the trumpet they didn't know if the help would arrive at LanternWaste (where the pevensies first appeared in Narnia) or if they would arrive at Cair Peravel(sp? The castle of the Pevensies) or they may arrive at the Stone Table, all were ancient and considered magical or something like that. So they sent Trumpkin to Cair Peravel to meet them if they should come there, and Pattertwig was sent to LanternWaste to meet them if they should arrive there, the rest of the ARMY was already camped at the Stone Table so they didn't need a scout to go there.