Small transport Captain reported encountering wake turbulence from the preceding aircraft upon takeoff. The passenger in the copilot seat then grabbed the yoke and attempted to perform dangerous maneuvers that would have worsened the condition. The Captain pushed the passenger's hands off the yoke and maintained positive control of the aircraft; and calmed the passenger.

Narrative

I was departing Runway 9 at BOS. I was cleared for takeoff; right turn 140. I began to turn right; I encountered some wake turbulence from the preceding aircraft. The aircraft burbled" a little and rolled right further. The passenger in the copilot seat grabbed the yoke with his right hand; and attempted to pull and put in left aileron. I maintained positive control of the aircraft; pushed their hand off; and told them "no." At a safe altitude I explained that it was just a wake turbulence encounter and there was no reason for them to panic. As they looked young and I understood their fear in turbulence I elected to continue the flight. However; this was extremely dangerous; these are the opposite control inputs for a stall/spin to the right on takeoff; and would have exacerbated that condition. In fact if they had pulled aggressively enough at low altitude and airspeed they could have caused a takeoff stall at an unrecoverable altitude and killed us. I believe the passenger was not trained in upset recovery; if they thought there was a loss of control inflight with a right roll; the correct input should have been lower the angle of attack and then re-orient the lift vector with the rudder. They were probably afraid of the ground rush. I did specifically write please put a small adult in the copilot seat on the passenger information list; although I believe this person was at least 16 - I could see their driver's license in their phone case - so I see why the Ramp Agent put them there. I do believe this passenger acted inappropriately; only 10 minutes before this event I had explained to them that they should not be touching the flight controls. I will not fly that passenger in the front seat ever again."