I did a little digging of my own and it seems that Interceptor is the only real whole tank treatment available. Other people have dipped corals in an insecticide and that did the trick, but it is not for whole tank use.
Even if you don't have a dog, you can explain your situation to the vet and they may write you the script. They just don't want to give it to you to use on a dog they haven't seen. It's my understanding that if you give heavy doses to a dog with mature heartworms (instead of just using it to destroy larvae), it can kill the dog. If the vet knows you know this, and know the legitimate reason you want it, they may give it to you. Still their discretion though!