freeze some milk in a form so you can crush it easily, when you need cold milk, get the frozen milk and crush it (more surface aria) then put the crushed frozen milk into a funnel with a coffee filter in it (the filter is to stop you getting chips of milk in your cereal) and then pour the milk through the funnel. Don't forget to put more milk in the freezer for next time.
This could also be done with frozen water but that could effect the taste of the milk. You will have to experiment with how much frozen milk to non frozen is needed
one possible way of freezing the milk so you can crush it is by putting it in freezer bags and laying them down so that it forms a thin sheet when frozen.
another idea is freeze a half full bottle of milk on its side or better diagonally if you can so there is the largest surface of milk open to the air. when you need to chill room temp milk, pour exactly the right amount of milk into the bottle. swirl and shake it (not too much as you will mix air into the milk and you will get too much milk) then pour it out slowly, frozen side down. Then put it back in the freezer
i don't how long milk is still fresh when frozen so you may need to occasionally replace the frozen milk. I say only put the milk you want to use in the "chilling bottle" as mixing milk from different containers can reduce the life of the milk plus you would have to then either freeze the remainder milk or use the rest of the unfrozen milk before the frozen defrosts otherwise you will have to replace it. this will work for 2% or less, i dont know at what percentage of fat milk can no longer be frozen in a domestic freezer.