Dent puller hole fix?
 

I have a 1994 f150 xlt ext cab I'm prepping for paint, I had a large dent in my passger side ext cab panel I managed to pull out with a self tapping screw. (I know I know ghetto way of doing things) but I didn't see a reason to buy a puller when I had this at the house. Now I have holes in my panel, I understand that I can mig weld these holes shut. My problem is I read that I have to have a backing such as a pre80s penny, but I can not get to the rear of the holes (or I would have pushed the dent out). Can anyone give me advice on how to fill these holes up?

Spray foam and body filler. Kinda mickey mouse, but if all else fails....

If you're popping a dent out with a self tapping screw, duck tape would be the obvious choice to close the holes.