A kit will probably make the closest thing to a Koppaberg, since it has artifical flavourings and sweetners in it. I made a pear cider kit which tasted very much like the Koppaberg version.
If you choose to use the fruits, you could brew your cider first. Wash, dry, and freeze the fruit (this breaks down the cell walls to allow for better flavour extraction, or buy a couple of bags of frozen fruit), then thaw before adding to your secondary FV. You might want to add a campden or something the day before, but I didn't bother, the alcohol in the cider should have killed anything still hanging around in the fruit. Rack the cider onto the fruit and leave for a couple of weeks or until the hydrometer readings are stable. Rack off the fruit and continue as normal.
I also tried a raspberry and lime cider using the Polish raspberry fruit syrup, and a lime squeezed in, and some lime peel. It has turned out quite nice, but would need a bit of sweetening to make it taste more like the commercial version. I like it dry though, now I find Koppaberg far too sweet :sick:
If you use fruit, you'll probably need to add some pectolase too.