You can get little plugs from a hardware store for a temp fix, just paint them to match the car. Thats what I did to see if I liked the wingless look.
If you want to do it properly you mig weld the holes shut, grind them down, then a thin skin of filler, then prime then paint. If you just use filler, it will bubble from moisture after a while.
you could also put a peice of tape on the outside and 2 part epoxy glue the inside. IF- you dont have access to a welder