JKB could probably rig up a solar panel and series of capacitors and find some way to 'energize' the outside metal of the feeder just enough so GBH gets a little voltage tickle/jolt when deciding to stand up there..
Or I noticed in buildings by us they have these flat aluminum trays with a series of vertical tines or spikes sticking up. They put them in window sills of tall buildings and it keeps the birds from landing there.
Lots of do it yourself ideas here at this link:
