Bacon grease might just attract more ants--grease ants this time.
I can't get a feel for how big your feeder is... Is the plastic jelly container almost as big as the inside of the feeder? If it is, I'd put a small amount of water in the bottom of the old jelly holder, then put a smaller dish (holding jelly) inside the larger container. The water will act as a moat to keep the ants off the sweets as long as the smaller container doesn't touch the edges of the larger. You don't even need enough water to float the smaller container--as long as water laps up around the bottom on all sides, it'll keep the ants out. Just make sure the water doesn't evaporate during the day...