I was thinking about this a while back. I guess the way the GM mechanics did it was to use a hacksaw
and small screwdriver etc. I agree, it looks kinda ugly. I was wondering if you could do something similar as removing the idle tubes in the book. Drill a hole (.100?) and then screw in a drywall screw. Then, using a propane torch, heat up the area real good. Then, carefully pry them out with a set of wire cutters. Not sure of the press fit in the aluminum base plate but i'm sure they are in there pretty good. I think just drilling them out could possibly work but maybe not due to the possible interference with the idle screw itself. Maybe a combination of drilling and heating and tapping/threading and pulling. Just ideas.
Dont know for sure as I have never seen these plugs actually installed.