Scott, the guy formally known as FlatheadManic I think hes Karp now gave me a bunch of ear plugs a few years back. I use them from time to time still (although I've only got 3 full sized ones left) What I typically do is cut them in to very small peices about the size of a kernal of corn and then soak them in anise. It works, but I've never used them solo. I use the foam for the floating factor, not the bait factor its just an added benefit.
Doing this is not a new practice Paylakers will use a styrofoam bead as the "pickup" or hookbait when fishing packbait. So really all that is being fed to the carp is the packbait (loose feed that is tightly packed around the hookbait or pickup). I've seen people catch carp on Partridge Artificial pop-up corn........fake corn really.......with nothing else. No flavorings, etc. I personally think it's more of a visual thing than a scent thing. But.......your on the right track soaking sponge in flavoring