Using a fence energizer for specific application

I do photos of birds in flight, coming and going from feeders. Squirrels are a problem as they take the feed the birds are coming for. I got a Patriot PE2 fence energizer and set it up as directed. Problem is the squirrel has to be both on the ground and touching the energized feeder to get a little shock. They soon learn to just jump on the feeder. I wondered if there was a way to charge the feeder, and I would control that charge with a switch and only use it when the squirrel was on the feeder. I don't want to hurt them, only give them the small jolt that this unit provides.

I know this is not your usual question but hope to get some help.