Here's a thought: If you're going to have your writer make up sentences for their spelling or vocab words, go for who can be the funniest or the weirdest and still convey the meaning of the word.
I guess that's obvious. But especially in regular school, it's often just about writing the easiest, shortest, most obvious sentence so you can get the darn thing turned in and get credit for it. It can get so boring and awful for everyone. If kids are trying to be funny, they're writing for an audience besides the teacher, and they're writing with a purpose beyond showing that they know how to use a word correctly. They're writing to entertain. The results have to be better than the alternative.
This is not exactly the same thing, but when I taught high school, I sometimes gave partial credit for wrong answers if they made me laugh. I hated giving short answer quizzes and getting them back completely empty, which wasn't unusual since so many kids didn't do their reading homework. It got so depressing. So I started telling kids to write something no matter what, and if it was funny or creative, they'd get a point or two for trying. And then we'd all get to laugh when I read the best answers to the class. It was better than crying.