I used to buy whole milk when it came on special. (Used to way back when!) I would freeze the bags. Then mix it half and half with reconstitued powdered milk.
I'll explain for those of you who are sitting there saying... "Wha?? Bags??"
In Quebec and eastern Ontario, we can buy our milk in 3 plastic bags (that total up to 4 litres). Yes we can get it in plastic bottles and cartons as well, but when you want a gallon ... you get 4 litres. I'll post pictures later.
In the meanwhile, with 4 kids in the house I used to buy powdered milk, and mix it with whole milk. Due to refridgerator space I would freeze the extra bags. I found when you defrosted them the cream separated but a whiz in the blender took care of that.
You could give your cream a zap in a blender or hand held mixer - you would just have to be careful to stop before "butter"....