Well, yes...
F&S
Yes, your scenario is possible. We've had occasional amusing "episodes" where passengers being screened into Tulla have had items confiscated. Had they secreted said items in the aircraft.....well...
Your potential scenario is possibly one of the reasons that the recent white paper has recommended changing pre-flight screening for pax to include flights on turboprop a/c with a max T/O weight of 20T (which wont include either the Q300 or Saabs, btw).
But there are plenty of other ways someone can get prohibited items inside a passenger terminal.
Cheers,
DIVOSH!