I think he is a another BBC journalist or part of the Top Gear Team you know like the support staff-mechanic's that took part in the 24 hrs of Silverstone and other challenges, I believe i have seen him in other episodes in the audience or or when they show the staff in challenges
even if the bbc do suspect that we know who the stig is and have to use someone else, we wont notice because the good thing about having a driver that doesnt reveal his identity is that you can use several drivers under the same identity, they'll only get a new stig if ben collins or someone actually reveals it himself by saying, "oh look internet people! i am the stig!"