Ribby and Flourpots,
I have no special trick! (just what you wanted to hear, huh?
A 14" straight blade spatula, a 4-cup glass measuring cup of boiling water, and a couple of bar towels are my best friends in the kitchen! Lol!
Let the blade heat up in the boiling water, take it out and QUICKLY run each side of the blade on the towel to wipe off water and use it to smooth the BC. You get two well placed strokes on the cake, one from each side of the blade, then do it all over. Dip, wipe, smooth, repeat. You shouldn't be actually pressing into the BC to smooth it, as you'll take off too much and that's not the goal. You want to smooth what's there. Smooth with a light, quick hand. Takes practice...good luck!