Ok, vacuum doesn't work. I even fashioned a nice attachment out straws. The vac actually started picking up oil, so the attachment worked well.
That passage goes pretty much straight down, so I don't think there is any chance of picking it up from the top.
I have one of the other earplugs sitting in gasoline, so I'll check to see if it dissolves by tomorrow. While I'm waiting for that, my next course of action is to drain the oil and to try and flush the plug out of the bottom.
I'm thinking that I should fill the block to the brim with oil, so I can get some force behind the plug. Thoughts?