I live in an old house -- can I squirt aerosol insulation into area behind faceplate before I attach new faceplates?

Many of the faceplates in our 1936 colonial are missing (because I took them off to paint baseboards. They’re two-prong AC plugs—I believe they have no ground. Can I, before replacing the faceplates, inject some aerosol insulation in the space behind the faceplates? There’s quite a draft that enters from the missing faceplates right now.