the first thing i think of is maybe printing the letters out on paper, and use that as a template to cut your letters out in the fondant?
That's what I was going to suggest...print out the letters in the size you want, roll fondant and put it on a cutting board (not on your vinyl or silicone mat), lay the paper on top of it and cut with an xacto knife. When you're done, let it dry a while on the cutting board so it doesn't stretch out of shape when you pick it up to put it on the cake.
I would print out the letters and try to use color flow
Oh I love this cake, I may have to borrow it for my boss.