You could make an ant moat to place between the hook and the feeder. The moat would be filled with water and ants will hesitate crossing it (although sometimes swarms sacrifice themselves to make a bridge).

Still... if you can find a lid to a wide jar (I've used a plastic Maxwell House instant coffee lid), you can try making your own - punch a hole in, thread the hanger through the hole, seal around it with some clear aquarium sealant, fill with water, and finally re-hang the nectar resevoir on the hook below the moat. Hopefully that will keep many of the creepy crawlies (at least the non-fliers) away from the feeder port.

Here are the plans for a simple ant moat you can make out of a
small can:

Here is a link that might be useful: Ant moat plan