is possible but not in a conventional way.
The Aprilaire and similar humidifiers depend on the heat from a forced air furnace to evaporate the water and blow it throughout the living space.
As one of the best attributes of a radiant system is its silent delivery of radiant heat it would be a shame to spoil the quiet. Since you are not blowing air around your space you do not suffer the same dehumidification caused by infiltration that a scorched air system does. Obviously you are still too dry.
Focusing on the upper floor one could get by with a conventional or high velocity - air conditioning only - system that would dehumidify nicely and cool your lower level if one is open to the other by a staircase say. Unless you have a lot of solar gain on the lower floor I think you will find this satisfactory.
As for humidification you will need heated -by electricity humidifier that could be used in conjunction with your AC air-handler at a very low fan setting - (not so good with HiV).
Or do as my Grandma did and hang a little water can next to or on the radiators and don't turn on the exhaust fan when showering in winter.
Oh yes and cooking pasta is good for just about everything and nearly a religious experience for me.