Bees are hammering my neighbor's hummingbird feeder — how do I call them off?

Third year, four hives in the North Carolina piedmont, and we're in that ugly gap before goldenrod really opens. My neighbor (lovely woman, endless patience) texted me a photo of her hummingbird feeder absolutely covered in my bees. Dozens of them, hummingbirds can't get near it. I know it's the dearth talking — that feeder is basically an open bucket of 1:4 syrup from a bee's point of view. But what actually works to redirect them? I offered to buy her a new feeder. Do the bee-guard port things actually work? Should I be feeding my own hives in-hive to take the edge off, or does that just make more robbers? I really don't want this to become a neighbor problem.