I need some good standing core exercises for my cardio-kick class?

I have a strength section in the routine as of right now I am building my business and can't buy equipment. I know of plenty of floor exercises for the core but I really don't want to get on the floor during the class. I have mostly pretty fit people coming to my class right now so something that is able to be modified for less fit individuals but challenging for my fellow advanced pole fitness students would be great or even a free place to find videos that will help me find a few good exercises. Thanks!