If the responsibility for operating an overwing exit is ultimately left to the ABP who paid for or was operationally required to be moved into the seat, then surely the cheapest extra safety measure is to (as well as briefing said pax), explain their operation to the rest of the pax during the preflight safety speil (I know, I know!). Just because there is not enough pax to have to fill the exit rows , or no one has paid extra for them , shouldn't automatically discount their use.