| Looking at the photo, can you not create a lever type movement to pull them out failing Yeti's suggestion..
Get the head of a screwdriver behind the plug, hopefully without touvhing the frame, then rest a piece of wood across the frame, and use that as a pivot to lever them free?
The string idea sounds like a great one, but as Yeti has said it's going to have to be strong, and an even pull to get them to move. | 
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