Havew used blu tack many times but thin about how pourous foam is.You'll never gewt it to work alone.Try Scotch brand hooks that have and adhesive that is supposed to not damage paint.Uses compound and tension of same to hjold.You'd need a few.Me I'd maybe make one hole and hang it like picture with wire if you can super glue wire to foam which is iffy.Scotch hangers at Home Depot is what I'd try first.
Cheers
Chazz
Cheers
Chazz