Oh, you know, you can cheat. While running around the class, you can say: "No no, this is not quite right, let me show you one more time. You see, it's like this..."
Of course, you explain as you do, since you are teaching! And, of course, do not "steal" someone's partner too often or for too much time. Keep running, you are teaching!
And do not forget, explaining a technique in details is a mental form of training.
Of course, sometimes, when the number of students attending the class is uneven, you have the opportunity to grab a lonely soul and let them train with you. Of course again, practicing a technique means learning to give it, and also to receive it.
See? With a little creativity, you can teach and train.