You couldn't exclude anyone on anything as ambiguous as smell (even before you add 2T oil into it).
Proper fuel testing is expensive and difficult. I mean, it's easy to identify Methanol or Ethanol vs Petrol, but it's quite difficult to prove a sample is a particular type of petrol (and therefore legal or illegal).
Considering what you CAN legally use, I can't see anyone being chased for using a race fuel or octane booster or any of that.