
Couldn't be him, they raced on Top Gear, Tim was in the Porsche and The Stig in the Aston (The Stig won!) and also, while The Stig was racing, Sabine was on the side of the track talking to Jeremy and Hammond (Captain Slow was gagged in the locker room).
The Stig also raced Sabine on one of Jeremy's videos around the Ascari race track.
As for the thought that there may be more than one Stig, that's not really a smart one, even if they would use a double for some shots, The Stig that everyone wants to know, is the one that does the laps and, as they said, for that they needed a tamed racing driver that could pull consistent lap times. More than one Stig would have resulted in gaps between lap times on the Top Gear circuit and you can see in every show that the driving style is always the same.