you can make a jig for a drill press..
and drill out every body fastener bolt down the center with a 9/32 drill bit..you will still get the fasterners holding power but it will be hollow and it will all add up..
you could do it to just about every bolt every fastener holding hardware on the body of the car..
you said something thats free..and not really destroy the car...
its easy enough youll just need cutting fluid and lots of beer..
cheapst