piperboy84, good question. Having grown up in the USSR, I'd say the vast majority of the population wouldn't even want to escape, and of those who would, very few would think of such a method. Also, the purpose of these flying clubs was to raise very patriotically-minded boys for the Air Force, so their ideological spirit was contrary to the idea of using the aircraft to escape.
By the way, few Berlin Wall escapes were so dramatic. With proper planning, it was possible to execute it in a much safer way. Again, the first and strongest line of defence against escapes was the Communist propaganda.