Well yea, this works for for me most of the time. You need to set a laptime, and I think you also need to then beat it. Then move (but not wise to delete in case you need to replace it) the PB folder out of the games main savegame folder to some backup folder anywhere on your harddrive, such as 'TaKeN's F1 PB Saves' folder, but leave the autosave folder.
C:\Users\yourname\Documents\My Games\FormulaOne/savegame/PB188003.000_e00008ecefe4850b_0
What I do is set my first laptime. Then I beat that laptime, (ghost is still easy to get past at this stage as it's usually when I've first learnt the track and nowhere near my fastest), and then I move the PB folders out. Then I can select any ghost to race from the leaderboard.
What happens then is a message comes up saying 'ghost lap autoload failed' (meaning it can't find my PB ghost), and then it downloads the ghost I selected. Or I can simply not select a ghost to race, and then do laps with no ghost.
I usually find that once I've beaten my PB again, a new ghost appears along with a new PB folder. You can move that out and replace the old PB folder in your backup folder. It's actually really quick to do once you know which folders to go to.