If they are like mine hamguy, there should be a little indentation on every other flat on the hex shape. They just push on. I found it necessary to gently message the indents with a round head punch to make them fit a little more snug.
I guess our posts overlapped hamguy. You are referring to the permanently attached nut covers. I just looked at mine, they definitly go on from the outside. You may have to pull the wheel cover to see what kind of attachment is on the inside. Sorry can't be of more help.