I don't know much about these competion things, so my idea might be useless...but people sure seem impressed with dogs who can "read"...Somewhere on this site is a thread about teaching yor dog to "read"...
My own dog does a card trick, but he uses my eyebrows and my hand positions, and cannot really "read" the cards, of course.
You could hold up giant sized placards, so the judges can see the word, too. Maybe some easy ones, the dog reads sit or rollover or something..then have one that is fancy, like your dog walks backwards or something.
To make it funny, train your dog to do something wrong, hmmm, i can't think of good example, but if you think on it, maybe you will get idea, so that everyone LAFFS at what the dog does in response to the word you hold up.
Like, so it looks like the dog is disagreeing, or having his OWN interpretation of your sign's word, phrase or question, to make everyone laff..... but i can't think of good example right now...Anybody got idea? you know what i mean ?
Your last card could say, "Do you think we won, Dude?" and he could jump around, stand up on his hind legs and bark, or, go get a toy trophy prop or giant sized blue ribbon and bring it to you, or nod his head "yes" or something...
Or you could have a sign that says "Are you tired yet, Dude?" and Dude would lay down and play dead. You could take easy moves and put a funny-ish question to the easy move.
You could use your leg positioning, your face, the way you hold the card in your hands, to help Dude distinguish between the commands, even though i have heard dogs can learn to recognize word shapes themselves.