I wouldn't recommend compound chocolate in this application. It's not very good tasting and I only use compond chocolate sparingly when no one is going to eat much of it. How about using an inexpensive chocolate, for instance the 'Sams' Club' in my area sells a 10# bag of chocolate chips for around $7.oo (I beleive).
You realize that if it's totally hard (so it looks good for you) it will just break off in big chunks when the person cuts it? I don't quite know what you have in mind, but my first choice would be to glaze it instead of using chocolate. If I really wanted chocolate to flavor it, I'd use a marbled pound cake recipe instead, or put mini chocolate chips in your current recipe.
I think a stiffer ganache would work(75% chocolate 25% cream) or even just thinning chocolate with some butter(or even chocolate chips with the butter). Problem I've had with the chocolate glazes(pate a glacer dark) is that the loaf sucks up the moisture in the glaze and it turns brittle after a day.
I've used Carma, and it's fine for a little drizzle, but if you plan to cover the top of the cake in chocolate, it's greasy! Angry's idea of mixing butter w/ choc. sounds good; it will soften the chocolate up a bit.
2 other ideas:
1. Maybe you can make a sort-of tent with cellophane, so that it doesn't touch the top, and this way, you cna have a nice gooey glaze.
2. Do a gooey glaze, and top it with chocolate shavings, so that it doesn't stick to the wrapping.