Both the foaming insulation foam and making Gorilla glue foam work, but are a lot heavier than 1lb styrofoam.
I repaired a speed limit plane last week using G Glue. All the seams around the center boom/motor block and the foam plastic had split. It came out plenty strong, but just the glue added an ounce and a half, as did some carbon fiber/epoxy to reinforce the boom/trailing edge joint.
It's not easier, but cutting a few foam blanks will let you get the plane nearly back to its brand new weight. Short chunks can be spliced in for bad dings.