I have to confess, I gave up on lay down. It was just too hard with little dogs. And really, it's not that entertaining of a trick. Is there any cute behavior that your dog already does? For example, when Lucy gets really excited, she bounces up and down. I was able to put a verbal cue to that (and then eventually just a hand motion-like dribbling a basketball) to get her to do it on command.
How about this Yorkie's bag of tricks:
(though the humans could use to crack out the vacuum!)
Teresa