How about doing away with trucks altogether, and have a fixed gantry under which every aircraft passed as part of the taxy. Since there's a mandated maximum width of aircraft, then having a gantry wider than this with downward facing sprinklers below it would enable aircraft to be fully de-iced both wings at a time without fear of missing a wing or missing a section. Traffic lights on the gantry would allow control. Would eventually be cheaper than vehicles as well, and would be yet another aide-memoire for those trying to take off from the taxyway too.