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.