Welcome to my favorite alternative head, shoulders, knees and toes!
I sing the song normally, but I won't make you suffer through that. I sing and act it out very slowly for my parent-tot classes. You will be surprised how many pick it up fast! Make sure you practice, practice, practice before you sing with a class (especially with parents!)
I also love to use this one for my school-aged field trips. It is a great gathering time activity when we switch from one activity to another. I gather them with the song (do it one time slow, and then one time fast to challenge them). Once they have sung, the attention is on you and you have time to explain the rules of the next activity.