If LHS PNF/PM wanted to take control he grabs his SS, presses and holds down the takeover button and says the usual, "I have control". The aircraft is under the control of the LHS SS all the time he has that button down.
Done it in the sim, practising baulked landings by RHS in case, as has happened, they freeze on the RHS SS.
I repeat my 535 post as no 330 capt has disputed my 320 view that the RHS SS is visible from the LHS even if the lighting is down. You just have to look across the flight deck. OK when the capt appeared from the bunk he would struggle to see either SS from the jumpseat.