Cap Cazzie/Cassie Casps Cape/Caper Caps Cappy Caspy
Chaldea (I think this is what Casper is derived from) Cassander
or, my favourite, Caspian (yes, Narnia, I know).
Or of course, you can nickname something entirely unrelated, as often happens in families (e.g. Lolly, Queenie, Bugs, due to a sweet tooth, attitude, hobby or some forgotten incident from which a nickname sticks). Or a nickname derived from the middle or last name.