E, can you get to a grocery store bakery? Since it's tomorrow, I'd just buy some
dark chocolate buttercream from them and ice with that. I usually buy a pound and that's always more than enough.
I think buttercream holds an edge very nicely.
Had Wilton not screwed around with their candy chocolate disks, I would have told you to melt those and pipe it out. Worked beautifully for the GBH 2 years ago and was horrible for last year's GBH. They changed it to melt much thinner so you can't pipe it.