How do you stabilize whipped cream to frost a cake?

I was given this tip several years ago by a dear "Master Cook", add 1 3 1/2 oz. package instant chocolate pudding to 1 quart of whipping cream, will keep in the refrigerator for SEVERAL days. No need to add sweetener, and doesn't really add a chocolate flavor. Needless to say you would have to calculate for the size of your cake and amount of whipping cream. Works every time.

Boulangere is so right, a swiss meringue is a great option. I wanted to give you the link to a whipped cream icing that I make its easy to work with and stable http://www.food52.com/recipes/11619_whipped_cream_frosting
You make a paste by cooking powdered sugar, cornstarch and heavy cream, let it cool and add it while you are whipping the cream. Its really a wonderful icing.

Thanks, boulangere. I would love to hear more about the swiss buttercream you mention. I tried one and it was a bit heavy/greasy. Also, how long do you think a whipped cream-frosted cake would stay looking pretty/fresh? I don't need to fuss with piping. I will decorate it with fruit and/or flowers. Thanks!

Wow, I admire your bravery. The easiest (and most flavorful) way to sweeten and stabilize whipped cream to use on a cake is to add 1 generous tablespoon of confectioner's sugar for each 8 ounces of whipping cream. Whip the cream to the soft peak stage, then add the powdered sugar and continue whipping to medium peak. The action of spreading the whipped cream will further "whip" it. I've made I don't know how many wedding cakes, and the icing I use most often (when not rolled fondant) is Swiss meringue buttercream. It's extremely stable at room temp for easily 4 hours. Are you familiar with it? I'd be glad to send simple directions if you're not. The simple butter and powdered sugar frosting is really the only one here into which you could incorporate creme fraiche. It would, in fact, loosen it up nicely. Otherwise it tends to be sort of mortar-like - difficult to spread easily, and very hard to achieve some nice piping effects. I hope some of this helps you, and hots off to you!