If you are concerned about the warpage.... how about attaching your small sheet metal patches with
the 3M auto body repair adhesives that they market...?
Body shops are using this stuff for major body repairs and manufacturers are starting to use it,too. They replace whole quarter panels with it, so I suspect it would be just fine for attaching your little hole patches.
Then just skim coat the repaired hole and feather it in as normally done..
