If you go to an auto paint store you can buy "structual panel adhesive" and do your patch the right way with proven automotive products. Yes you can "glue" these panels in, is done every day in the manufacturing and repair of automobiles.
BMW even has a repair bulletin for the 2004-06 5-Series where you glue the frame rail in! No welding what so ever, only glue!
Here is a bulletin from GM on gluing in a patch panel.
http://members.aol.com/whatcouldiknow/gluepatchpanel.jpg Brian
