I just pulled out my Joy of Cooking and checked out the substitutions section. It says for whole milk, you can use:
For one cup of milk=1 cup of water and 1.5 teaspoons of butter (icky).
For one quart of milk=1 quart skim milk, and 3 tablespoons of cream.
I have NOT tried either of these, just pulled them out of the book
Good Luck!