Bummer David. Do you know what a Socket- out is? You would need a machinist friend that would have one. They are slightly tapered hex tools that you tap into a bad socket, then turn it to extract the bad item. That is an option but they sometimes do not do the trick either. Those set screws that cover the pins are notorious for being over tightened and seized in. When you put it back, do yourself a favor and only lightly tighten it and use some Moly as well. Or just find a rubber plug and occasionally check your pin.
Now for the ugly way to remove the plug if an easy-out/ socket-out is not an option.
Get a drill bit around the same diameter as the width of the hex wrench that should take it out. A 5mm I think. Drill out the bad center of the plug being careful not to push too hard. When you break through, you don't want to damage the pin's hex socket too badly.
Now find a socket head bolt that has a bit larger diam. than the hole you just drilled. Grind a hex or square or even a triangle on the end so that the edges angle to the left a bit if possible to bite in. Tap that in the plug and unscrew the plug. All the tapping should have loosened it up and it should come out. If not,,,you could be very very careful and heat up the surrounding aluminum.
Good luck.