Method 1 - Play through the level Uprising until you get to the first outdoor area, then proceed and kill the Brutes. Head through until you get to the large area containing a Spectre full of Brutes. Kill the Brutes without destroying the Spectre (make sure you have one or two Ghosts remaining to use). From the entrance to the Spectre area, drive the Ghost up the wall on the right. A bit of nose-wiggling may be required. Park the Ghost in the small corner and then return by jumping onto a tall rock and slide down to get up the second Ghost (this Ghost is not required but it does help).