I am not sure if you want something to show up in your combat log, or just be able to see the cast bar. Pitbull is a unit frame addon that allows you to have cast bars under all the unit frames. The can be sized and such for however you want them. This works for your own frame, target frame, target of target frame, party frame, and even raid frames. If you want to get real crazy you can have targets of party members, main tank, main tank target, focus target, target of focus, so on and so on. There is a lot of options here.