Pretty sure Oswald's arm wasn't paralyzed and could bend and raise at the elbow. There's your first clue.
Now, can somebody produce a re-enact of Randle's exact view of Oswald as she watched him carry the package. And how long did she watch him and was her observation of him unbroken, continuous, or did she just glance. After all, no reason to study a package unless something gave an onlooker an impression that the carrier of said package was attempting to at least partially conceal it. Not too smart carrying a package that might appear sizable enough to carry a rifle on the day that the POTUS was scheduled to ride around downtown in a freakin' convertible.