Hey, I'm new to the whole Speech thing, (SOOO Great!! Wish I had found it before my junior year tough )

Anyway, I have a dilemma.
I'm and going into my second local tounament next week, doing this HI peice called "Santaland Diaries" by David Sedaris, about working as a Macy's elf, and at one point he uses sign language when talking to deaf children ("Sorry, but Santa has a tumor in his head the size of an olive") Great line, but only one problem: I don't know sign language...

So what should I do? Try to fake it or cut it? Would it be offensive to make up sign language?