How long will homemade frosting last?

First let me say HAPPY HALLOWEEN! Now onto the important things... So you know I made that huge cake for my mom and dads anniversary. And I made the Mexican Hot chocolate Buttercream for the frosting on the top and bottom cakes. When I read the reviews it said the recipe made "twice as much" frosting as needed. So instead of doubling the recipe like I did for the cake, I just made an normal batch of the frosting thinking it would work out perfect. Oh boy, "twice as much" was a understatement to say the least! Upon frosting a six and ten inch layer cake, I piled the left over buttercream into a gallon sized zip lock baggy...and it filled it more than half way, that is a 1/2 gallon of frosting. But, I thought, "no big deal, Mike's birthday is this week. He wanted a yellow cake with chocolate frosting so I'll just use this, perfect". NOT. Mike decided that he didn't want a homemade fancy from scratch cake, he wanted a plain old, out of the box cake with package frosting. Mike loves my cooking, he hates package food like casseroles, etc. But he said he just didn't want anything "fancy". I started to explain that nothing was fancy, I'd make a basic yellow cake out of the BHG Cookbook, and he had already said the frosting made with fine chocolate was good. So what's the deal? Anyway, I dropped it, it was his birthday.

So now I'm left with roughly $10 worth of frosting. Yes, that is right, the entire batch was easily $20 worth of fine organic ingredients. Metric is deceiving, 500 militers of Egg whites = roughly 1 dozen egg whites (you read that right, I separated 12 eggs in one sitting). 900 grams of butter = approximately 1 lb. of butter. You get the idea. Not that I minded spending the money, that's not the point. I just don't feel good about throwing it out. I already 86ed the yolks and felt bad about it. So what do I do with all this frosting? Will it freeze? I used about 1/2 a cup of it to frost the boy's Halloween cookies, but I don't have any other cake-warranting events in the near future. Should I just make dozens and dozens of cupcakes for the office? Really, any ideas, I'll take 'em!!