Indeed not. On one analysis post about the Cave Troll there was an indication of muliple Cave Troll accounts syncronizing with witness voting. If the Cave Trolls get a good faction on the Witness Circle of Twenty then barring software solutions could become a reality.
Remember that voting for choice of witnesses is weighted as well. A whale has more say than those at the bottom of the tank.
With only approximately 4% of accounts voting on Witnesses such a faction need not be comprised of an unrealistic amount of whales to tilt the voting scales in their favor.