the back of my bench has a round platform, i put a chair behind it and set up plates around me before i start my set. i stack the plates on my lap and do seated calve raises. its almost like the free wieght version of the seated calve raises. this week i did 7 45's and a five for two sets of 6.  you can do standing calve raises with a barbell off the floor let you heels come down almost to the floor but just do not release tension on the calves.  also you can put a heavy dumbell in your belt and do one leg calve raises or two legs at a time.  you could do donkey calve raises but hard to get enough wieght with only a heavy dumbell.  front calve raises can be done with a barbell seated or you do do them with a dumbell in your belt off a step.