We've burned molasses in there, and poured it on the bait. I tried using cheap grape pop, too.
That sweatshirt you can see hanging from a tree in the background is actually a barrel (with a sweatshirt around it, to keep out crows and such) full of old lobster shells, mackerel fillets, and smelts that are full of spawn. It stinks to high heaven and seems to attract attention.
That radio trick is really smart. If I had some sort of timer I could use to make it only work from about 10 pm to about 7 am that would be perfect.