With all of the effort you put into reading and trying to use our 四字熟語, imaginary readership, you might find yourself tempted to try and make jokes using them, or out of them. My advice is this: Don't.
Now that I'm back in Japan but not yet regularly employed, one of the things that I've been doing to make ends meet is working at a local bakery. I've actually been able to use a number of yo-jis in the course of conversation there:
切磋琢磨: (re: learning Japanese so I can shove it in Brett's face)
孤軍奮闘: (re: the boss's joke that I would have to come in to work tomorrow, even though the rest of the company has a day off)
画竜点睛: (re: the chocolate cream breads that someone (me) tried to put out for display before the chocolate cream was in them)
But today, when we were making these cow face cream pastries (モウモウクリーム), and I noticed that the chocolate ear spot had fallen off of one, the head bakery dude (パン長?) said 「いいよ。色々な牛がいるから、」and I replied 「そうですね。十牛十色,」 I may have taken things too far.
If you want to joke with your 四字熟語, there are a couple of things you want to make sure of first.
One is that the target of the joke knows you well enough to figure out that you are in fact, making a joke, and not just retarded. I've mentioned before the frustration of the non-native speaker in Japan. If you say something that doesn't match up to their imagined responses, Japanese people around you are more likely to assume that you made a mistake than to try to figure out if what you said has another meaning.
The second thing is that your yoji-juku-joke is an established one. Your best bet is to go with one of the common jokes that we've mentioned before in the comments, but would be good to include in a real post.
There's 焼肉定食, infamous for being the answer most Japanese students provide when given the following problem: Complete this 四字熟語：＿肉＿食.
And then there's 鹿素麺, which is a mangling of 四面楚歌.
Do you know of any other humor-fied yoji out there?