I did the same as you...a trial pair, about 3 weeks before the cake was done, just to make sure I knew what I was doing. :-) I'm really glad I did, because when I made the final pair a week or so before the cake was done, I ended up making a couple of minor changes from my first pair.
I used a 50/50 fondant gumpaste mix, and they turned out well and dried hard as nails. If you have an extruder, it works great for the laces.