It's not a great idea. Cream tends to separate when frozen, and while you can freeze a carton of cream (double-wrapping in freezer bags is recommended), you can also shake it thoroughly after it thaws to reblend it (although it will not be as good as new). With cream cubes, you're likely to have a block of frozen water on the bottom and a crumbly layer of butterfat/milk solids on top. Jumble them around in a freezer bag and you'll wind up with a mess that's not very easy to use.
The greater problem, though, is that cream is so eager to soak up other flavors. Some people will notice it picking up an off taste from the ice cube tray itself. Then, unless you can really isolate the cream cubes from other freezer smells by double/triple/quadruple bagging and sucking all the air out of the bags each time you reach in for a cube, it will quickly taste stale. It will be cheaper and less frustrating to purchase cream in the smallest carton you can find, and if you have enough, make a double batch of whatever you're cooking and freeze that for later or give the spare to a deserving friend.